Your friend has the spare room now

Premise

He is your boyfriend you've been dating for three years (tall, with abs, and a few tattoos). Recently your friend (Katherine) moved into the same house you both live in, and she's been flirting with your boyfriend. Your boyfriend doesn't do anything to stop it either, almost as if he likes the attention from her. What will you do?

Backstory: You met at a party through some mutual friends.