Something I Never Thought I'd Do

I generally don't like talking about sex in public and especially on this blog, as it doesn't really relate to recovery. Except it does. Sex is very stressful and very exciting and very relaxing. No matter who I'm with, it's all of those things. I'm always worried that I'm not doing enough to pleasure the guy. Also I can't really orgasm so I usually want it to last as short as possible. 
On my bucket list is Threesome. It's only sort of on my bucket list because I never thought I'd get the opportunity, and because I'm not sure how I would feel about it. I told Chris about this and agreed to do a threesome with him should he ever find someone. That happened about six months ago. 
Yesterday, Chris was talking with one of his (and my) friends. A guy at his fraternity. They were discussing threesomes and how each of them was trying to find someone to do one with, and suddenly they came up with the bright idea of a foursome. Chris, Marius, Cosette and I. Obviously I'm using fake names there, just in case. 
They asked me if I was in and I said yes, thinking I would have at least a week to prepare myself for going so out of my comfort zone. And giving me time to back out if I needed it. But when all four of us were discussing it, we decided to do it TODAY. And that's the story of how later today, Emily is going to be having sex with three other people in the basement of a fraternity. 
On the one hand, I'm excited. There is a reason I said yes, after all. Cosette is really hot and I've been wanting to experiment with her. When I first met Marius I liked him and thought he might make a good potential boyfriend. I haven't had sex in a long time, so I really really really want to have sex. And I like both Cosette and Marius's personalities. I was reading online about how some people just want to have a threesome. They care who it is in terms of "he would be good to have sex with" but the goal in mind is the threesome, not the specific person. That's not how I feel about this at all. I want to do this specifically with them, they're not just props. 
On the other hand, WHAT THE FUCK AM I DOING??? First of all, I've never done *anything* like this before. I've never kissed a girl. I've never had sex with someone I didn't love. I've never been watched. I've never involved more than two people at all. How the heck do you go about a foursome? I feel like I'm underprepared for a test that's coming up, and there's no way I can study. 
Second of all, Cosette and Marius are waaaay hotter than Chris and I. Well, I suppose I can't really speak for Chris, because I don't know what Cosette thinks of him, and I think he's attractive. But objectively, I'm very much of an ugly duckling compared to Cosette. I'm not as built. I'm not tan. I have marks all over my legs because I scratch my mosquito bites until they bleed. When I walk my thighs jiggle a little bit. I don't have huge boobs or really perky boobs. My teeth are too big. I laugh really weirdly. I don't have long slender fingers. This makes me feel anxious because what if no one wants me? What if I'm relegated to the corner, sort of a pity case? 
Third, Cosette is a stripper. So she has experience dancing, kissing women, and playing with them. And she has experience doing this with really hot women. I don't think I'll be able to please her. 
Fourth, what if I can't please anyone? I have no idea what Marius likes. He could be a sex god. And due to my lack of experience I could just be really bad at it for him. I'm going to be worse than Cosette anyway. That's a given because she's his girlfriend. 
Fifth, Marius and I have never had anything like a sexual relationship. For one, he's Devyn's old roommate, so he was off limits when I was pursuing Devyn, and he also had a steady girlfriend, so that automatically made me unattracted to him. It's just really weird to think of Marius in such a platonic way one minute and then the next I've signed myself up to have sex with him. I also feel weird about it because I still have some remnant feelings for Devyn, and even though I know I can never go back to that again, I would feel like I'm betraying him by doing things with his roommate. The roommate of the man I love will have seen more of my body than the man I love. That's a really weird thought to me. 

So how does this impact recovery? It's stressing me out, which brings out behaviors. I wrote about it in my journal but I feel like I need to post it, even if no one responds. 
Advice would be appreciated though, if anyone doesn't feel too awkward.