I need some real good advice?

I live with my lady friend she is 46 I am 51. recently her 26yr daughter and her 4 children moved in with us. She was against my wishes having guys over and now she is pregnant from this guy she had know maybe a month before she found out she was pregnant. Well you can guess what happened next. Turns out the guy has a wife and kids. Of her 4 exsisting children there are 3 different fathers all of whom dont pay any child support. No she brought home another guy of the street and are all sleeping in the same small room. The problem is, it is driving my realationship into the groung. What can I do? my girlfriend of course stands by her daughter. and when I mention my dislike of this situation she makes me out like I am evil or some thing. I feel like just leaving but I do love her very much. I think her daughter is a common with no thought given to the lifes her ever growing family will have to live. She is on Welfare but as you know that does not last forever. Can anyone Please help me I am going nuts over this