This isn't alimony - this is property division. I know it sounds pedantic, but there IS a difference and it matters. So yes - it looks like the payments are permanent, lifetime and would not end upon her remarrying or cohabitating.
Also, this is a stipulated agreement (as opposed to being ordered by the court), where both parties willingly agreed to the terms.
If he wants to reopen the property division, he'll need an attorney - and it could get expensive (that's if it's even possible at this point). I do not rate his chances of changing the terms and I think it would be a very expensive lesson in futility.
It could also end up with him losing even more, financially, in the long term.

