Its a bad situation and you can't expect every guy to just respect you like they have in the past. I agree that they should expect it to always be a no by default until she either verbally says yes or its obvious by her actions and reciprocation intent that she is fine with it.
You shoyld learn this lesson to tell a guy, look I'm not interested in having sex with you. If he keeps trying then have a game plan to get out of the situation safely. Get a cab/Uber or call your boyfriend to come get you and your friend. It will be better to have your boyfriend annoyed or mad that he had to pick you up but it's better than telling him later that you ended up having unwanted sex with the creep because he wouldnt take a hint.
I feel bad for you. It sucks that this happened. Dont let it taint you with other guys, just be more on guard with guys if you plan to share a room with them in the future.
You probably saved your friend from being violated by him but you didn't protect yourself from the same danger.
The thing is you also taught this guy a lesson that he doesn't need concent, women just want him. Thats what he thinks now. So you endanger future women who he hangs out with. If you had told him no, you are not interested repeatedly he might have stopped but if he didn't you could have a legal case against him.
As it is right now you have very little to no legal case. A lawyer would ask you these same questions we have been asking you. Why didn't you say no? Why didn't you get out of there? Why did you get a room with this guy? Why did you continue to drink with him? Why did you continue to lay in the same bed with him? Why not move to the floor/couch/chair?
All your answers favor this guy that you didn't do enough to stop his advances. Sure you didn't say yes but you never said no. A simple no. No jury, no judge and no prosecuting attorney would want to touch your case because you didn't do enough to protect yourself.
I bet your boyfriend will feel the same way. He might wonder now if you go anywhere that guys can easily get you to have sex with them because you are not brave enough to say no. Or to make your intentions very clear that you don't want sex.
Once again I feel for you. But all you can do now is take these lessons and grow from them. I still don't think you should tell your boyfriend but that's up to you if you can't keep it from him and decide to tell him. It might not end well. Youll be hurting once again.
I would cut all communication with this guy and make sure your friends know. He might not be a bad guy but he's not a good guy either. He might be confused by the whole thing himself. Who knows. Maybe he doesn't remember because he was too drunk. But I wouldn't continue trying to find out from him. Just ignore him and cut him out of your life.