I read this one a long time ago. It’s completed and I wanted to reread it. It’s about a man who shares his home/apartment with another guy. They’re not close and the roommate is a buff, scary type. One day the roommate brings a girl to come live with them and introduces her as his girlfriend. It’s a smut so MC hears/peeked at them being intimate. Later the roommate has to leave and tells MC to take care of the girl. MC ends up sleeping with the girl until the roommate comes back. The girl has some sort of history and I think she is hiding from a group of people or something.