I'm sorry this hurts, but... you knew that he sucks, and is in general not a trustworthy person. You did your best, but you can't make him not a sucky dude. This isn't your fault, just like the other thing wasn't your fault. He's just a lame, crappy dude.
I'm sorry. Lean on your family, they'll be of tremendous support. May I suggest that you don't involve your daughter in your marital issues? Let her know that you love her and that you're working things out and that no matter what, everything will be ok. It puts too much stress on children to hear about their parents marital issues.
Oh my gosh, I'm so sorry for you both, especially your DD. Please don't feel bad to be asking your family for help. Your parents and brother sound like they care a lot and want to support you.