What to do about my girlfreind?

My girlfreind has really bad relationhsip problems with her mother, for the past year and half i have constantly supported her through this and i'll be honest i am getting tired of it. I have never met her mother but from what my girl tells me she is quite selfish and only fouces on her own problems, she has always neglected my girlfreind. My girlfreind has been depressed and finding life difficult, her mother has not supported her at all. I have to support my girl freind all alone, I just cant see things getting better. Part of me wants to just leave the relationship. Is that such a bad thing?