My girlfriend's overly dependent best friend

Hi there. I'm new to the forums and I guess I'll start off on a sort of painful note here. I've been seeing my girlfriend for nearly 6 months now. We're long distance currently, but plan to move in together in May or June once her lease is up in her current apartment. When I'm there, she's all about me; we're practically attached at the hip, but we don't make a big fuss over each other either. We spend quality time together without going overboard. It's very nice and during those times, I always feel confident that our relationship will last.

However, she lives with her best friend and the relationship that they have is not very good. She has told me on multiple occasions that her friend is dependent on her, has serious jealousy issues even though they are only friends, among other complaints. Her friend, who I know quite well, also expresses a general dislike toward me now that we are dating (we were friends before all of this and back then, things were completely different; we all got along very well). Whenever I'm not around, I find that my girlfriend's best friend takes her out a lot: to dinner, to movies, to events, etc. It makes me feel quite uncomfortable, but I have dismissed it for the sheer fact that they have known each other since they were 4 years old.

Whether my girlfriend is cheating or not, I think this relationship is toxic. Not only is her friend very dependent on her presence and assumes that she will always be around (we are all adults, mind you, at 22, 22, and 21). My girlfriend complains about this a lot, saying that she is tired of being a mother-like figure to her best friend, yet she does nothing to correct the behavior. She hasn't even told her friend that she plans to move in with me in several months!

I guess what I'm seeking is some sort of advice. It seems my girlfriend is rather serious about me, already bringing up the idea of marriage and spending the rest of our lives together. This reassures me to some degree, but I don't know how genuine her sentiment is. Perhaps I am over thinking things (which I do tend to do).

Any advice or personal stories are welcome!

 

Thanks for the advice! We actually sort of talked about it tonight and she agreed that she should tell her friend she is moving up here. They're going to have a conversation about it after her friend's finals!