How to deal with invading friend

So my boyfriend has this friend who he spends a lot of time with him. He doesn't like me, and i don't like him (but most of my boyfriends friends, and his family doesn't like him either). His friend, Brian, seems very clingy and emotionally unstable. my BF says the reason he doesn't like me and acts the way he does (more on that later) is because he cant have with my boyfriend what me and him do, instead he is stuck in friendzone by my boyfriend.

- so a little about this friend Brian: he has known my BF for years, as far as i know they used to hookup when they were young but remained friends because when my BF was young and had family issues due to coming out as gay probably or whatever, he was that friend that provided him a place to drink and crash and let out all the crap teens hold when they go through tough times like these. they never dated just hooked up before i guess, but i know he isn't cheating on me with him or anything, that was all in the past over 5 or more years ago. Brian recently started posting a lot of crap on Facebook tagging my bf whenever they hang out, sharing memories all the time specifically with him and he never done that before we got really close romantically. he does that because he tries to get under my skin or compete for my boyfriends attention. a lot of people don't like him because he drinks a lot, does a lot of pills, and just bad life choices. acts like a child even though he is well over 30. 35 or something.

- problem is my bf knows how bad Brian is. he warned me i should stay away from him because he is manipulative, and very selfish. he is the one friend my bf doesn't want me to meet because how bad he is. i know it may seem like he is hiding something suspicious but knowing them both, its not about cheating. i see my bf once or twice a week because i work night shifts so i don't have that much time, while him and Brian hang out almost every day. one day though i stayed the night over and in the morning was hanging out with my bf when Brian kept wanting to come over but he kept telling him no because he is with me, yet he still showed up, he had to lock the door. he threw a fit because he couldn't hang out with my bf one day when i don't see my bf for days and deserve to see him. one of my friends suggested the relationship them 2 have like that is because my bf doesn't know how to say no, but he does, Brian just doesn't listen. my bf also seems to be extremely committed to people in his life, Brian helped him when he was young, so he kept him around as a friend, even with how bad he got.

- how do i deal with this? i told him it bothers me a little that he spends so much time with him and how Brian treats me, he doesn't do anything directly, he just does things like flaunt their time together as in like "haha i got him today, not you" and its extremely irritating. i cant tell him to not hang out with him, i'm not gonna control his life, but i want to make him want to distance himself from Brian just a bit. he says don't let it bother you but if it gets worse, he will take measures. thing is it cant get worse its already bad enough the way it is for me.