I need assistance HELP!

How do I tell my boyfriend that I’m a little jealous of one of his oldest girl friends? Like I don’t wanna come off like a bits cause I truly love her she super sweet and kind but like he’s always with her and at first I thought nah they’re just really good friends but like she recently got a boyfriend and suddenly my boyfriend hates that guy and I find that kind fishy and just now I was saying bye to him and we were making out he brought her up some how and I was like what the heck obviously in my head not out loud but yea I just want to get it out and not have it stuck inside but idk how to do it without making it weird.

HELP