My roommate has been masturbaiting while I'm in the room, wtf do I do
TLDR in the title, but for context I started college a bit less than 2 months ago. I (18F) met my roommate (18M) through the roommate selection process, and over summer we became friends just playing video games together. We live in a fairly nice dorm at our college, we have a private bathroom and shower and its big for college dorm standards, but its still just a single small room with only about 6 feet between the beds. My roommate has occasionally said they were taking naps and put up a big pillow they have that obscures them alot, which I thought nothing of until yesterday. They said they were taking another nap and I still thought nothing of it, until I climbed into my bed to watch youtube because I was cold, when I looked over, they were watching porn and their blanket was moving up and down as you could guess. I very much tried to ignore it, and gave them the benefit of the doubt that they forgot I was here, until a few hours ago when I saw their blanket moving up and down in the same way while I knew they knew I was there.
I don't dislike my roommate, but I am terrified of talking to them about this, and this whole thing makes me really uncomfortable with them doing that while I'm in the room. I don't know what the hell to do.
Edit: I will probably try to talk with my roommate about it sometime over the weekend, I don't want to jump directly to reporting them to Ra's or anything because I don't necessarily want them to actually get in trouble, but I will if I really have to. Also get popcorn for one of these reply chains because it is some of the funniest mental gymnastics I've seen.
Edit 2: They started doing it again, so I finally talked to them and they agreed not to do while I'm in the room anymore. But all they said was "its a good boundary to set" which is like sure, but an apology would have been nice too. I'm still pissed overall that its a thing that had to be discussed in the first place. Also I acknowledge that this is a horribly worded post, I wrote this fresh off a draining test so I was tired, but the replies are hilarious so I'm not changing it, though it is unfortunately a true story.