She is his stepmother after all, she should be quite capable of looking after him. I had two stepsons to look after and would have utterly mortified if mum had thought I couldn't do it. You are still going to be mum whatever happens, the best thing is your son's happiness, going that route will make things much worse in the long run and all sorts of problems will start. Leave well alone and start thinking of son instead of yourself and get out and about yourself, and have some you time.