Try again or let go?

I had a boyfriend who is now the soon to be father of my child, however during the first 5 months of my pregnancy we broke up, he would smoke weed and drink often & it was not something I was okay with at all, so he started lying and hiding it from me & my attitude wasn’t the best. We argued a lot especially because we are still so young, & having a baby was not in our plans! our relationship became unhealthy so about after a month of breaking up, he found someone else... that he says doesn’t fight with him, that drinks and smokes with him. They’ve been together for about 4 months now, but he tells me he’ll always “love” and have a “soft” spot for me. I’m expected to give birth around March 23,

& I’m more than willing to try things again, especially for my baby & simply because I still love him.

It’s been hard caring a pregnancy alone, but I’ve managed so far, idk if I should make an attempt and fight back for him, or just keep trying to forget him and let go?

I find it hard to talk about this with anyone.. so any advice would be highly appreciated !