Arsh, I can only say that I'd feel exactly the same as you do. I still don't understand why your daughters have to sleep at his place. Why can't he bring them back at the end of the day? I know he has the right to partial custody but they're so young. Why can't he agree to do what's best for them? Forcing them to sleep in a strange house without their mom is cruel even if he's their father. It seems everyone has to adapt to his preferences which isn't fair. Anyway you already know all that. Currently I'm ok with being friendly with my husband because we're not yet divorced but if we divorce I believe I'll feel the same as you - bitter and angry. I can totally see how you went from depressed to angry. If there's anything you can do to make this situation work more in your daughter's favor before the divorce is final it'd be worth pursuing unless you've already done so.
