Divorce Support Forums: married to a gambler -debt?- custody of stepchild?

My husband opened up a PO Box and checking account without my knowledge. He's racked up credit card debt with cards in his name to the tune of ??? I'm sure in the tens of thousands of dollars range. How do I know? Credit card companies calling demanding payment, now lawyer's offices calling me at work since I'm a "lead". He tells me it's none of my business. In the meantime, the house is in my name with his mother as a co-signer. The debt I have on the credit cards in my name is about $40k and was incurred jointly. I would claim $8k of it to be solely mine, but the rest has definitely been a joint effort for all kinds of reasons. He doesn't deny this at all. Divorce has been on the table seriously for over a year, and I feel we are reaching an end. I want to hold it together until the school year is done. His 10-year old daughter lives with us full time (she is one of my most favorite people in the world) and I really would like her to have the stability until summer and then all hell can break loose. Her mom is irresponsible (drugs, alcohol, sleeps around when not in jail), I don't know where my stepdaughter would end up living. Her dad works from 2am - 8:30pm a lot of days running mail. Her grandmother also works nights as a night nurse. My stepdaughter's parents weren't ever married, so there was no divorce, no custody awarded, no parenting plan in place. Do you suppose it would be possible that I could get custody? Also, what would be my responsibility to his unknown debt? I would like to get all my issues straight before moving forward. Thanks for any advice.