Repeated from your duplicate thread in the "Marriage" sub forum:
He doesn't move on and end it with you because you let him use you for whatever it is he's getting from you; sex, financial aid, a proper roof over his head? If your boys are under 18 then there is child support to pay... perhaps that's why he stays with you ... just to avoid paying it? Whatever. He uses her for sex of a different "rush" then he gets from you.
WHY DON'T YOU leave him and stop letting him use you and abuse you? What is stopping you from just making a decision about your own life instead of leaving your life in his hands to misuse as he pleases?
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion