Does it still count as rebound?

It truly is an awful feeling when an ex starts dating someone else and I think what complicates matters for you is that he was so indecisive as to your break up.
All breaks ups from long term relationships are incredibly hard and having a child with that person usually means that you still have to have contact with them and thats not easy. It sounds like in some ways you are still holding on hope that the two of you will get back together and I think given how suddenly and recently the break up happened that's completly understandable.
I think for now though you need to focus on yourself, your wellbeing and that of your child.
Try to be kind and patient with yourself. If possible reach out to family and friends for support and distraction during this time.
If he does come back again uncertain whether he wants to be with you again, my advise would be to tell him that unless he is certain then he shouldn't be playing with your emotions like that. If it was me i wouldn't get involved with him romantically again unless he was willing to commit and work through the issues and if he is not willing to do that then I think that shows he is not the guy for you and although it is hard that you be better of being single so when the right guy does come into your life you will be available for him.
Take care and try to look after yourself.

I think it might be a rebound. I think he's trying to get over you, but believe me, if he really loves you, he'll come back. No doubt about it. I wouldn't worry too much about it. Look out for your child. If it lasts for a long time though, I would suggest moving on. I know it won't be easy, but I believe you can do it. If you ever want to talk, feel free to message me ^_^