My boyfriend is having a friend from out of state staying at his place for 5 days

I'm a little paranoid that my BF is having a friend from another state (who's also gay) staying over at his place. I just think the whole thing is a little weird. He's coming specifically to visit him. I don't know their history other than they were best friends in college.Granted, we are in an open relationship, but outside of us we are supposed to be having mindless, one-time hook-ups and not seeing anyone like that. My BF had visited him a month ago when he was in his state for work, so it's not like he hasn't seen him a long time.