Good for you Cathy for being able to "SEE" what his agenda really is.
I'd also suggest that you make statements instead of asking him leading questions that he'll either balk at, give you a lie or half truth for a response, or immediately say NO because NO is so easy for them to say.
If you need him to watch your son, say on Thursday night to go have dinner with friends or run to the store (whatever) say, "H, I need you to stay with son Thursday night from whenever to whenever I have something to do." (DO NOT TELL HIM WHAT). Ths forces him to MAKE a decision/commitment. He's either going to say, "NO" or "Okay" If you give him any wiggle room with your request, he'll find plenty of wiggle room for his answer. Be prepared if he says, "No I can't do it." To say, "Okay, no problem, so and so said she'd watch him if you wouldn't." And STAY UPBEAT when you say it so he'll know HE can't control you or YOUR whereabouts with his NO. T2
