New and would appreciate some advice please!

Hi, I am a single mother of a seven year old daughter.  I have been separated from her father for 2 ½ years now (he wanted time to think about what he wanted!) and divorced now from him.  While we were separated I found out 2 ½ months down the line he had met someone else, moved in with them shortly afterwards and they now have a 9 month year old daughter between them.  My ex’s partner has a child from a previous relationship.  Since our split I have been struggling to get any payments from him.  We had agreed a payment and that was ad hoc now all he is paying me is what he wants.  The last payment I had was in May!  He is probably gonna argue the fact that he shouldn’t need to pay cos since they moved in together (December 2010) he has her half the week, but also he should be paying me back for the time he has asked the childminder we use during term time to pick up our daughter cos he can’t anymore, and he isn’t.  He has our daughter Thursday and Friday when we use the childminder and I pay for it.  I get the tax credits of course, but should he be paying for it?  Do I stand a chance to get what I deserve?  In the beginning he really put me through bad times with the way he treated me, took antidepressants to help with the stress (luckily now I don't and have got someone special in my life - fourth time lucky!) and now he is still doing it.  Can someone please help me with some advice – I would really appreciate it.  Thanks!