OP, I feel like some of the comments in here are really making excuses and blaming you. You know what happened. Don't let anyone, including yourself, minimize the severity of what occurred. You owe Alex nothing and comments on here claiming that filing a police report and potentially pressing charges is overkill (or "burning" as one person stated) are victim blaming idiots.

He probably wasn't drunk and confused who's room he was in. He probably wasn't sleepwalking. You shouldn't act on theories, you need to act based on what you know.

What you do know is what happened was very scary and you need to treat it seriously. Even if you don't want to file a police report and charge him with anything, I really think you should. This is probably not his last rodeo. Sexual harassment and sexual assault are not usually committed once by a perpetrator.

I know it sucks to stir the pot and you just want the situation to resolve, but the situation isn't going to be taken seriously unless you take it seriously. What happened is extremely horrific, and you should be more concerned about making sure this guy doesn't victimize anyone else than making sure your roommates side with you.

Also, if your roommates blame you for what Alex did, they're not good people anyway. I know I would side with someone who takes the situation seriously and isn't flippant about it. Which, by the way, I don't think you're being flippant, but not calling the police and filing a report is brushing it under the rug and minimizes the severity of the situation. Consider this, if this happened to one of your friends, what advice would you give your friend? Probably, you would tell your friend to call the police immediately and let them make the judgement call on how to best handle the situation.