new here. Custody question

Annplus1

Hi. I have been lurking for awhile, and really like the support I see for each other.

Backstory, then question- about 2 months ago, my STBXH decided he didn't want to be married anymore, and that his life will only be good if we got divorced. Two weeks later I determined I am pregnant. I am currently 16 weeks along. STBXH moved out a few weeks ago, and has decided it's time to move forward with the divorce.

 That is the very shortened verison of my story. It also includes a drug habit, very curious behavior regarding where he was at night until 1-2am on week nights, etc. I didn't ever get evidence of an affair, but to be very honest, I didn't look very hard. The behavior came on very fast, and we got into therapy, but he quit when the therapist told him to grow up. After that, everything was my fault- in his brain.

At the end of the day, we dated for 6 years, and were married for 4. For 3 years we tried for this baby, and while the timing is terrible, I am very excited. But now concerned. I know to document any drug use, but as he states it's over now (sure) not really sure how to do that.

 I also need advice on what to ask for/bring up in mediation regarding custody. I am in MN, and I know I need to rely on the mediator's guidance, but want to know any thing I should ask about while there.

Thanks in advance. I am pretty sure we will be getting to know each other pretty well. I don't have any other children, and this is all pretty overwhelming.