if you don't have a lawyer already...get one...I'd see about putting up servailance cameras around the house that tape, that way you have proof of his commings and goings. Also I would audio tape any phone conversations with him so you have proof of his lies.
I'm not sure about the laws where you are, but here in Iowa, as long as one party is aware of the servailance, it is admissable in court, but even if it isn't admissable where you are, the "evidence" will be great leverage when it comes to custody and proving his irresponsability in the care of your children.
I hope this helps, and good luck to you.
Maybe i'll get lucky and in my next life I can be a dog!!!