Envy [19F]

I've been in a relationship with my boyfriend, who's 24, for nearly a year now. Our first date was interrupted when his best friend's girlfriend got too intoxicated and needed a ride home, so he went to pick her up. Since then, he’s had her location to help his friend keep an eye on her, as she often drinks excessively and can act irresponsibly. I've noticed that she’s very attractive, and during our time together, I’ve caught my boyfriend looking at her inappropriately, which bothers me. I’ve asked him to knock it off because it makes me uncomfortable, even though we still hang out with them quite often. The other night, while we were all drinking, she fell asleep on our couch. To wake her up, my boyfriend started tickling her feet and playfully wrestling with her, which made me extremely uneasy. When we play games, she never participates when I’m around, but somehow she always ends up playing with him when I’m not home. At times, my boyfriend talks about her more than he does about his best friend, and I know they might just be having fun, but I can't shake off my jealousy. I'm curious how others have dealt with similar feelings—how did you manage to overcome your jealousy?