I'm trying to be happy with things the way they are?

If you think he's cheating, dump him. If he is cheating, marrying him WON'T make it stop. If you are convinced he is not cheating, and you feel like having , come on to him. We guys are not mind readers, and EVERY time my wife comes on to me, I am ready, willing and able. He is likely wondering why you don't want to have anymore, and he does not want to feel like he is pressuring you.