When an ex spouse fails to follow the court's orders (which includes your divorce decree) then your remedy is to take the ex spouse in front of the judge. The judge has the ability to enforce her orders by using various means, ranging from a mere warning to awarding attorney's fees to jail time.
I have recently had two cases where the clients waited a year or so to take any action against their non-complying ex spouse. Each case was with a different judge. Each judge asked the client why he/she waited so long to bring the issues before the court.
We ultimately received the relief we were requesting in both cases, but it is worth noting that the judges asked my clients about the delay. Many times a judge will see the delay as a sign that the issue is not that important to the client. And that fact can sometimes adversely affect your chances.
To the client, the judge's logic doesn't make sense. The client will say "Of course its important!" "Why do you think I paid my attorney a retainer?" "Do you think I like sitting in a courtroom with my ex?" And other statements. But the judge will look at your case from a completely different angle than you do.
So what to do if your ex is not following the court's order/decree?
1) Contact your ex and tell him what the problem is. Do it by email or letter so that you will have a record. Be specific about what he is not doing under the order/decree and give him a reasonable deadline to get it completed. Be direct and to the point. Do not insult him, talk about the new girlfriend, or that you and your bff know he was at Chili's last night. Stick to the issue and be finished. Keep any replies that he sends.
2) Hopefully #1 will solve the issue. If not, then you will need to speak with an attorney. Take your attorney all relevant paperwork from #1 as well as a copy of your order/decree.