Hi Delli. Firstly I'm sorry to hear about your situation. It's very hard at first and so soon after the split your emotions will of course be all over the place.
My advice to you is not to keep trying to start conversations with him about "Why?". Because that means you're being the needy one and putting him in the position of power. And no-one likes needy.
Instead in front of him you need to start pulling yourself together and show him that you've accepted his decision so you're going to start moving on.
You can do this by talking to him about putting routine into place for contact and a regular amount for maintenance.
Rule 1 of being a single parent is never to rely on your ex's money. Again it puts him in the position of power and he'll make you dance to his tune if he knows you're fucked without his cash.
That's not to say don't get money from him. Just don't rely on it to pay rent.
If he asks where you've gone just keep it vague like "I went out with friends"
Quite often he'll suddenly be interested again once he realises that instead of going down in flames and being the needy one that you are moving on. My ex did it to me. Wasn't interested until I moved on. Then suddenly she was.
Things will be difficult though when baby is so young. It's not like he can have him overnight easily so you will still have to see him a lot. But be strong in front of him and save any tears til you are alone.
Believe it or not things will get better and I would wager that eventually you'll actually enjoy being on your own without having to compromise for him.