
“Look I know you and (blank) are dating and he’s going to come over sometimes but I would appreciate it if you split time between here and his place more evenly. Also, did you give him a key at some point? Because I was never asked if he could have one and I’m not comfortable with how much he comes by when you’re not here. I’m not really asking a lot here I just want to be able to use the space I pay for too without him constantly being over.”
My only issue with that is the reason he’s able to get in is most likely he has a key OP doesn’t know about, which could cause issues if the landlord finds out as most leases are pretty strict about extra key copies. I do agree that making the boundary that he can’t come over or stay without her is a great place to start, but I would definitely want him to give that key back too.