Everything's falling apart an I'm always the pillar everyone leans on

I have always been the one to pick up the pieces and help everyone; including my parents.   The only times my mom calls me is when she is going through a mental break and thinks no one loves her etc and now that my mother has gotten worse (both mentally and physically)  my father has been leaning on me.  The whole 4 days I've been home for the holidays,  he's been venting to me and asking what he should do etc.  I tried to help as much as I could but honestly today before I left that  I don't want to talk about mom anymore.  He said it's cause he needs someone that  talk it through and he can't do it by himself; I told him I understand but both with him and mom I am the only one they come to where  they have problems and I can't be there for them. I have been there for them since I was a child and I have my own problems  that they're never there for.  I can't.  It's not fair and things seem to be falling apart fast.