First, there is a sticky at the top of this forum that deals with this issue. Had you read that you would have been better informed.
Second, this is NOT parental kidnapping. That occurs only when the child and a parent disappear without letting the other parent know where they are. Another factor of this is who has custody.
You said you "get back together" after the divorce, but you seemingly never remarried so this was not really getting back together. And now that he has a new girlfriend he is trying to get rid of you.
You indicated you gave custody to ONE of your children. Did a court affirm this arrangement? Was any visitation schedule set by the court?
All these factors are involved in determining what is legal here. But he cannot charge you with child abandonment, What he can try to do is eliminate any rights you have DUE to abandonment. Which means he would have to file a court petition to do so. This means a hearing where you can present your case. So you need to keep a journal of your attempts to see your son.
If you can supply additional info about the situation as I outlined, we may be able to help further.
I moved back in with my ex-husband after our divorce. We lived together and considered ourselfs in a relationship, but we did not get remarried. I have currrently married my daughter's father.
In our divorce papers it states that I have reasonable seasonable supervised visitation. Which nobody will tell me exactly what that means either. My ex-husband stated that it meant whenever he said it was okay, but he only said that after I started dating someone. He was letting me get my son every other weekend, but he has no gotten upset with me and doesn't want to let me or anyone from my family see him. I am just trying to learn a little more about all of the laws, so I have a clear understanding of them.