My Ex is now living with his girlfriend and she's not divorced yet

Well I just found out when my kids got home from their dad's place that my ex's girlfriend is living with him now.  In case noone knows my situation, my ex moved and and left us in December, 2007, he filed for divorce and our final hearing was March 18, 2008. (pretty recent) Anyways he told the boys about his girlfriend, (or whatever you want to call her) and they have been screwing around with each other since October, 2007.  Her divorce isn't final yet and she has 3 kids.  Apparently this weekend (and my ex didn't have the boys the whole weekend either he dropped them off early like usual)--he told my oldest boy that she is now living with him and he introduced her to the boys this weekend.  I felt it was too soon and told him, of course he doesn't care.  She doesn't have her kids with her, her husband has them, what a poor excuse for a mother that is!!  She chose a man (and a loser at that) over her own kids!!  Is there anything legally I can do with regards to visitation about this?  I was told that she can't spend the night over at their dad's place when the boys are over there for visitation.  I just want to know if there is anything I can do about this.  I know I need to log everything down with regards to visitation because he's not taking his visitation wtih them like what was ordered in Court.  I know I can take him back to court and file full custody and have support raised to.  I'm thinking of doing this because they are with me the majority of the time anyways.  Just need some advice on this please.