He feels no guilt for what he's done or is doing currently. The lump sum was done (hopefully) to get you to accept and ride off into the sunset, never to be heard again.
Mandy, I wouldn't accept the offer. Your son deserves better than this pittance. Go for what you feel is right that will keep your son living comfortably. Make sure that he can send the check to the bank or a solicitor so that you don't have to deal w/him all of the time about late payments, etc.
Stick to your guns on this one.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.