Oh goodness AB10, he's showing you his true colours now. From your first thread, it sounded like he would only offer sympathy and support for a limited period when you were struggling, and now, given the huge upset and upheaval he's inflicted on you, it's the same situation. Almost an eye roll and 'aren't you over this yet?' attitude. How dare he?
The fact is he chose to develop a relationship with another woman. He chose to put you and his son at the bottom of his priorities. He chose to say cruel things to hurt you, in order to justify his new relationship. He chose to walk away. He is now choosing to pick up where you left off, and he is choosing not to give you what you need in order to process what's happened.
He turned your life upside down with no warning and yet now, he's demanding that you decide what happens next NOW? He didn't give you warning of his bloody bombshell just before Christmas.
I know it's so easy for us who aren't part of your situation to give advice, but he doesn't deserve your tears or your love. If he were genuinely contrite and knew what he'd risked, he'd be letting you call the shots about if and when you can forgive him, not demanding that it's now or never. Even when he's done wrong, your forgiveness (or lack of) has to be all about him. He's a disgrace.
Stay strong. You sound lovely and your son is so blessed to have you. Rely on those you hold close and let them support you.