The thing that stands out is his lack of respect for your boundaries and acceptance of this being what you need right now.
IF there was ever any chance of you reconciling as a couple (although it doesn’t sound like there is) it would be through the long term re building of trust, respect, love and attraction. He would acknowledge that and give you the space and time to (hopefully) get to that place on your own through the rebuilding of your fundamental friendship and parenting relationship first.
He’s not prepared to do that, he wants what he wants and he wants it now and isn’t afraid to pressure and guilt trip you into it. That on its own would tell me that he hasn’t really changed, he may not cheat or take drugs (?) now but he hasn’t grown enough to respect your wants and needs alongside or above his own.
You don’t need a reason to not be with someone. “I just don’t want to” is enough. I had this after exh cheated on me - as if no matter what reason I gave it wasn’t enough. It was valid. It’s so disrespectful.
in your case I would grey rock any conversation about the relationship. Stick to one key phrase “I am not in love with you, I have moved on, I hope you can do the same”. Rinse and repeat.
Family come in all shapes and sizes, there’s nothing to feel guilty about that your family isn’t the traditional set up. Who knows, you may meet someone and you will have that in the future.
I would concentrate on all the good things you and your DS have, work on feeling good about your sons life as it is so that you are not tempted to do something you don’t really want to purely out of guilt.