Taking it up the pooper won’t make you gay. What makes you gay is if you’re physically and emotionally attracted to men. (If you’re attracted to both sexes, then you’re bi.)

Fooling around physically with another guy just to experiment does not mean you’re gay. It means you’re fun and enjoy trying new things.

OK.. so with that out of the way, here’s a few thoughts:

• There is a difference between MFM and MMF threesomes. Note where is the “F” and the two “M”s in the acronyms. A “MFM” threesome means there’s no touching between the guys. A “MMF” generally means there will be some touching and play between the guys as well as the girl. It sounds like your girlfriend is turned on by the thought of an “MMF” with you.
• It’s possible you won’t even be able to get hard. This happened to me with my first MMF (wife and I are swingers and she has a thing also for seeing me dominated by a guy), and it was kind of a surprise because I’d never had any erection issues previously. I think all the anxiety and worrying about it just caused my brain to shut things down. It wasn’t until my wife and the dude starting sucking me off together that I got hard again, and then every time it was my turn to do something to the guy… I’d go soft. I’m just sayin’.. be prepared for that. It’s normal.
• OK, down to business. Your girl wants to see you dominated. Does she expect you to kiss the other dude? Talk about it now, so you don’t get surprised. Does she just want to see you lying on the bed with a dude’s dick up your butt. Does she want to participate somehow in that part? Make sure you know exactly what she wants, so you can not only fulfill her fantasy, but also so you aren’t surprised in the moment and aren’t sure what to do.
• Don’t do ANYTHING you’re not comfortable with. If your girlfriend wants you to do something you really really don’t want to do, then tell her that you’re just not ready for it yet. If she keeps pushing, then honestly.. it’s a sign of a problem in your relationship that goes beyond sex. That being said, there’s nothing wrong with stepping out of your comfort zone, and it sounds like you’re game to try anything once… so that’s good.
• Sucking a guys dick is actually kind of fun and enlightening. Hopefully the other dude isn’t huge, because that would make things more difficult for your first time. Think about what you like, and then apply it to him. Start off licking and kissing, just teasing, etc. Then try to get the whole tip in your mouth. Ask your girl if she wants to suck the guys dick with you at the same time. Make it hot for her by touching her tongue with yours while you’re both licking the guy’s dick. She can lick his balls while you do his shaft. I’m not gay in the slightest, but I thoroughly enjoy giving a guy a nice blowjob. It’s fun! Cuming in your mouth is probably a bit much for your first time, so be sure to tell the guy you aren’t down for that. (Unless you are…) This way, there is no sudden surprise.
• How about getting it up the ass? First,… two words to live by. SLOW and LUBE. I’ll repeat that, because it’s super important. SLOW and LUBE. As in, make sure the dude goes SLOW SLOW SLOW and make sure you have a lot of LUBE. I find silicon lube works the best for butt stuff, because it’s just supper slippery and doesn’t dry out so fast as water-based lube. Get a big bottle of it and smear it everywhere. Use a lot of it. Make it your girlfriends job to apply the lube and keep applying it as the dude is going into you.
• A quick side note, that many straight guys love being pegged by their girl. So you might want to try that if you end up liking this stuff. 🙂 Try /r/pegging as they will have a lot of advice, I’m sure.
• Before the big night, I highly recommend you try a butt plug. Get a small one, with a big flange on the end. Don’t use a dildo or vibrator. The reason the end of a butt plug is flanged is because your ass has a tendency to “suck in” things once they get passed a certain point. You don’t want a trip to the hospital to extract a lost toy. Go to the sex store and ask for a beginner butt plug. One of those cheap silicon ones will be fine, since this is just for fun. (If you like this stuff, then you can invest some decent $$ in a better plug later.) It should be about 2 or three inches long and tapered on both ends (until it gets to the flanged part) so it’s easier to insert and remove.

Here’s the part where I also suggest you take a nice big shit before you start doing anything butt related. If you want, you can do an enima. Wipe yourself with baby wipes so there’s no smeared crap left over. Nobody likes a nasty poopy butt. Evern with this preparation, however, you should all be prepared for some poop to come out. It’s normal, and ya .. it’s a little gross. When it happens, just clean it up and continue. Fun sex is pretty messy sometimes.

Oh ya.. so put a towel down before you do anything. Don’t want to get your sheets all nasty, right?

And also… ALWAYS have the guy wear a condom if he’s going to be putting his dick into your butt. This is for safety and you must not ever skip this, no matter who says what. If the dude won’t wear a condom, then don’t let him near you. It doesn’t matter if he’s tested disease free. Wear a condom for butt sex. Period.

Moving on…

Oh ya.. the butt plug. So now you have a plug and you’ve got to get it inserted into your crapper. Take a shit to get as much out (or enema), and then lay down on your side. Pull one leg up towards your chest and put the other leg straight. Reach around to your asshole and smear a LOT of lube. (The towel under you will catch the excess.) Using too much lube is never enough. Smear lube on the butt plug, too. Now… relax. Don’t pucker your asshole. Try to relax and let your anus open up. It’s a muscle and is very difficult to control. You’ll feel it when your anus relaxes and it kind of “opens up”. Take your time. Go slow. Take your time. Did I mention there’s no hurry? Just relax.

Now position the lubed up butt plug at the opening of your asshole, and GENTLY start pushing the tip in. Your anus will most likely pucker up nice and tight. Just hold the butt plug there, and try to relax. Go slow. Relax some more, and eventually you’ll feel your anus open up again. Push the plug in a bit more. If you feel ANY pain then stop. Some mild discomfort is normal, and some guys actually like this a lot (like me), because once that plug gets all the way in, the “relief” feeling is awesome. For your first time.. just go very slow. Relax, maybe add some more lube if you need to. There’s no hurry.

Eventually, your ass will accept the butt plug past the half-way mark, and you’ll feel it get sucked up into your butt right to the flange. All done! Just continue to relax and enjoy the (hopefully) good sensation of something up your butt. Don’t move around too much. Just lie there and see how it feels. After a while, you can get up and the feeling will change.

Maybe try rubbing one out at this point, or have your girlfriend give you a blowjob for a job well done. You’ll find climaxing with something in your ass is quite a novel sensation. 🙂

Getting the butt plug out is a bit of a challenge. If you just yank it out, the odds of also sending a load of crap out is pretty high. Plus it doesn’t feel so great. What I found works well for me is to go sit on the toilet, grab the plug with one hand and then kind of pull with my hand while also pushing it out with my anus muscles as though I was actually pushing out a stubborn turd. It will usually pop out fairly easily that way, although be prepared for the tip to have some crap on it. Just wipe it with some TP and you’re done. Clean the butt plug with a good anti-bacterial cleaner asap. Make sure you wash your hands thoroughly.

• So now you’re ready to take a cock up your ass like a champ! It’s basically the same as the butt plug, but it’ll be bigger and so the dude should go slower. SLOW SLOW SLOW. Your butt hole is surprisingly elastic, and despite what you think.. that dick will fit. But just like it kind of hurts to squeeze out a massive solid turn that’s been in you for too long.. it will also kind of hurt to have a hard dick stuffed up your ass. GO SLOW and use a LOT of lube. If the guy is pushing to fast, then tell him to back the fuck up. Don’t grin and bare it like a man. That’s not cool. This should be fun and exciting and pleasurable for everyone, including you. You don’t want to get raped. You want to enjoy this. So tell him to GO SLOW, use a lot of lube.

Positions that are easiest for entry are the one I suggested for the butt plug (this is best for butt plugs because it gives you much easier access to your ass). You can also try sitting on his dick, as then you are 100% in control over the depth and speed of insertion. Rest on your knees and lower your ass onto his dick nice and slow.

You can also try getting into the doggy style position and opening up your ass as much as you can. Be very careful with this position, though, as it’s super easy for him to go too fast in this position and that will HURT like nothing you’ve ever felt before. (Unless you’ve been constipated for a week and torn your asshole while pushing out a 5″ diameter petrified log.) Another one that works is to lay back and bring your legs up to your chest. Again, make sure the dude goes SLOW and you have a lot of lube. These two positions are for more advanced ass play, so I don’t recommend them unless you and your girlfriend have already had some pegging experience…

(And make sure he wears a condom.)

Once he’s inside you, just tell him to hold the fuck still for a while. It’ll take some time for your very sensitive anus to adjust to having a giant log stuck in there. Your anus muscles will be going crazy because they’re trying to squeeze that dick out. You want to relax and just be still for a while to adjust and let your body figure out that all is ok.

After you’re comfortable, put some more lube in and then let him SLOWLY move in and out a little bit. You don’t want him pumping you like a jackhammer, as that will hurt you. Tell him to go slow.

If you are super lucky, he might just tickle your prostate, and you’ll actually have a p-gasm. That’s happened to me a few times, and it’s absolutely amazing. So you can enjoy butt sex as the receiver, too.

What I like most however, and I’m sure you will, too… is when my wife sucks me off while the dude’s dick (or butt plug) is in my ass. It’s just a very “full” feeling, and the eventual orgasm is tremendous. When he gets ready to pull out.. again, tell him to go slow. Some poop will probably fall out along with his dick. Just clean it up and continue. 🙂

Once again, condoms are necessary. This isn’t a porno, and you do NOT want a dude to stick his bareback dick in your ass and then fuck your girlfriend with that dick. That’s how sickness happens. As with any partner sharing situation, you should always change condoms every time you switch partners or holes. No exceptions.

I hope this is helpful. Be sure to come back and tell us how things went!

TL/DR: Go SLOW and use a LOT of lube. Don’t let the guy control the pace of entry. Don’t be afraid to tell him to slow down. Relax your anus as much as you can. GO SLOW.