So you think he sleeps with your every month, he has to give you money every month .. right?
(I try to understand your logic)
I would say your chance is even less. The longer you let him sleep with you, the less
money you are likely to get from him.
You two are not married. He can run away any time, be aware.
Sorry that I'm kind of blunt. But I just want to point out your position in his eyes.