Should I take over my mom's soon to be ex-husband's mortgage?

I've "helped" them soooo many times when they couldn't make it. I myself have been house hunting a year now. I want a duplex or side-byside, this wednesday i actually made an offer on one. Now this guy calls me asking me take %50 of the mortgage and i can have whatever company i want and take the big bedroom blah blah. If i was looking for a single family house i wouldn't buy this one, The only plus is the nice size lot, nice neighborhood but everthing else is too small. I tell him I'll call him back and he says he's just trying to keep his family (he has a 7yr old with my mom) together and I can ist in avoiding this horrible travesty. I don't want to. What should i do? I feel like i should help them becuase i AM able to.. like $$, but I;'ve been saving for 5 years. I am 21yrs old, this has been a goal of mine (2-family) and i'm soo close. I think its kind of messed up for him to get me involved in his debt and ask me to forget about me and what i want to do with my life and wait another 10 yrs before i can get what i want. but i feel bad letting him drown because i don't like the color of his boat, you know? any advice would be awesome, good or bad, mean or whatever. THANKS!