Please help! Bad situation for DS

kiley&matt

My STBXH has been taking my son only about one or two nights a month.  Our child support hearing is coming up in a few weeks, and he has suddenly taken an interest in having DS every other weekend.  I know this is because of the hearing, and I'm not sure I'm okay with it.  I found out about a month ago that STBXH is already dating someone, (we've only been split for two months, and we hadn't even filed for divorce at the time he started seeing her). 

 Yesterday, I stopped by the house while he was at work to get a few things that I had left there (he told me to keep my key and said that it was fine if I ever wanted to go there), and this b**** is there!  She must have been upstairs in bed, but it looks like she's living there.  Her stuff is in the shower and the medicine cabinet, and her clothes and stuff were all over the place.  There were shot glasses laying all over the place, and bottles of prescription pills. 

 I do not feel good about DS being in this environment.  First of all, I do not even know her, or what kind of a person she is.  Secondly, I don't want my almost one year old son accidentally getting his hands on a bottle of prescriptions or a shot glass.  What can I do in this situation?  I've told STBXH that I'm not comfortable with him taking Liam overnight if she's going to be there, and he flipped out and said that I'm trying to control his life and that he's not going to wait around for me to be ready for him to move on.  Then, he said that he was going to tell the court that I am trying to keep his son from him.  What do I do?  I'm supposed to drop DS off at his house tomorrow morning.  Can I legally not let him see his son or will that make me look bad?