My[f] roommate[m] has been jerking off in my room when he thinks I’m not home

My friend and I recently moved in together. To help save on rent. But I think some sexual tension is developing. We’ve been friends since early high school and there’s never been anything romantic or sexual between us but ever since we moved in together it feels like every time I turn around he’s masturbating. He doesn’t know I know but I keep almost walking in on him. One time I heard him master baiting in my room through the door. I’ll be honest I’m not sure what, if anything, to do about it.

I’ve also found cum on my pillow a couple times.
And if you have those times I didn’t notice right away so I ended up sleeping in it.