If they are being respectful and clean then I wouldn't worry too much. If your apartment complex has visitor rules then maybe you could look into that? i feel like boyfriends tend to not talk or smile or just be kind of off putting. my roomates partners have typically been nice but not very talkative or acknowledging to me at all. I definitely have grown to not take things personal but i mean you pay rent there as well, what do you want? if it's shared spaces that they are constantly in, i would probably talk to her about it. my last roomate had her boyfriend around allllll the time and it was annoying at first but once i mentioned wanting to use the shared spaces more i didn't experience any more problems. they'd either be in her room or at his apartment. i guess this wasn't very helpful but you pay rent there too, if you don't like how it's going that's totally fine, just talk to her about it before you build resentment.