Sometime I feel like I don't belong their

Well in the morning before school starts I hang out with three other friends but I always feel as if I'm out of the question. They always talk about stuff I'm not involved in (stuff I really don't know about) so I'm just their listening the MCR while they talk about a bunch of crap. Don't get me wrong but I think it's just one girl in the group causing me to be left out. For example( this happens all the time) : I would try to start a conversation that we can all talk about but then this girl seriously just intrupts the conversation which causes me to be left out of the equation. The reason why I hang out with them is because of one friend and we have been friends since the beginning of middle school. I don't want to just leave the group because I don't want her to feel like I betrayed her for some other friend. Believe me if my friend wasn't in the group then I would have never been in it. I know I don't belong there but I don't want my friend to think bad about me if I leave.