Alimony pay-off question

I have a friend that is divorced, and as part of her settlement will receive alimony for 42 months which would terminate if she were to re-marry. She went to the bank the other day, and her ex-husband deposited the remaining amount of alimony as a lump sum, she is barely over a year into receiving alimony.

The question is–is this irrevocable? If she re-marries, can he come after her for the amount that he would not have paid? Has he hurt himself by doing this? He has communicated nothing to her, other than a note left with the bank deposit that it was for the alimony settlement. She suspects that he is doing it to avoid a tax burden from the sale of real estate that occurred in May. Is there anything specific that she needs to do (or not do) with this money?

I do not see how the husband would go about obtaining repayment of alimony that he paid in advance of its due date. If a terminating event occurs before the end of the alimony, he could likely demand repayment and threaten suit if she does not comply. He is likely doing it so that she is taxed more heavily on the alimony and he gets a better tax deduction, but she should review the rules concerning alimony recapture as he may have to recapture some of the alimony paid in advance.