First of all, there is nothing you can do not to think of him 24/7...this is a process for you just as much as it is for him. Don't beat yourself up about it. as for backslides, everyone has done them at one time or another. Again, don't beat yourself up about it.
What to do? Nothing. Don't call him and if he does call, let him talk to the kids and be business as usual, be pleasant. Don't ask him any questions unless it has to do with the kids.
You haven't said anything about your situation so more information would be helpful.
One thing is for certain, if he hasn't given you any money, after March 6th he will probably HAVE TO by court mandate especially if you have kids.
Give us more details regarding your sitch and then we can give you the best answers from our own experience.
Hang in there!
Valentine
Aug '06: H moved out July '08: H had a kid with the OW May 12 '09: emancipation day
"Life moves pretty fast. You don't stop and look around once in a while, you could miss it." -Ferris Bueller