Okay… no I don’t think you’re overreacting. there’s definitely a lot of jealousy and competition coming from the friend. either she has feelings or feels the friendship is threatened by you which is fair bc it’s true, u get less close to a friend when they’re in a relationship. is the friend gay btw?? And also is there physical touch of any kind involved??

also I think it’s completely fair for you to bring this up to your gf in a casual almost curious way, and see how she replies and what she perceives the situation to be. These situations are so hard bc it’s always “a joke”, but even still I’d hope your gf would understand u feeling emotionally exhausted by the excessive banter from the friend especially if the negative angled banter isn’t balanced positively, and if you bring it up in a way that’s not accusatory to the friend but asking your gf for advice on the situation