What do I do?

I know the subject title might seem stupid but please hear me out. I was at a party and I hooked up with a friend (totally consensual) in his room. He then went downstairs to handle something (I don't remember) and someone else came into the room. I thought it was my friend so we had sex. When it was over I found out the guy wasn't who I thought he was. I freaked out and he left. Is this rape? I feel like he took advantage of me but I don't know what to do. I feel like I'm partially to blame, like I should've made sure it was my friend or something...

He definitely took advantage of your state. What happened with your friend? Did he come back in the room? Is it possible that he let the other guy come in? It's hard to say what really took place without more information, but I can see how you might feel guilty about this incident. I don't think you should let the guilt get to you too much though because what was done to you was wrong no matter how you look at it, just be more careful in the future. Unfortunately, we really have to be super careful who we trust because there are a lot of aweful people out there that do not have our best interest at heart. Parties are notorious for this sort of thing. I have seen many posts like this one. I'm really sorry that this happened to you. If you feel like you need to talk about it more, I'm listening