Is it okay if I tell my girlfriend that I don't want her sister to come over to our apartment?
Is there a reason for not wanting your girlfriend's sister coming over?
I'm getting sick of having her over constantly!
It is understandably not wanting your girlfriend's sister always coming over, but you should respect your girlfriend's feelings about who can come over. You should talk to you girlfriend and set some rites about who can come over and how much.
Why should I listen to her? I don't feel like we are in a relationship anymore.
Don't give up on your relationship before you at least sit down with her and talk about your issues. Let them know that the visitations are too much and to set some limits. I suggest you work through it and stay together for now.