non-modifable support

I am engaged to a man in Missouri who has to pay his x-wife alimony. He says it is "non-modifiable". When his set time is up, he says she can't ask for more nor can he ask to stop paying even if she re-marries before that time is up. He also has custody of thier two minor children. She does not pay any child support or anything thing else. I am wondering how all of this works. If one or both of the children decide they want to move in with their mother as they get older, can they do that? If they do, is he responsible to start paying her child support? I've never had to deal with anything like this so please offer any help you can.

Whether or not the children may end up with mom in the future is not predictable. If they do go, it will be the father's moral obligation and legal responsibility to support them.

hm

Should the mother gain custody at some future date and requested child support, it would, of course, be up to a judge to make the decision whether or not it would be ordered.

Be sure you can live with your fiance's situation BEFORE you marry him and further complicate his life.