OP I have been you in many ways. I was the 15 year old left standing with the baby. Though in my instance my ex didn’t want to get back together. He didn’t want to be a dad and I tried my hardest to encourage him and to facilitate a healthy relationship with his son but sadly he just wasn’t capable of being/didnt want to be the father he could have been to our son.
Long story short, he now lives abroad, DS has ‘fond’ memories of the times his dad did xy and z (the very few occasions he ‘bothered’/was forced by his mother to spend time with him in the early years), whilst also hating him for leaving him and having nothing to do with him anymore. And a broken relationship between DS dad and DS grandmother as she tried desperately to make my ex be a dad too.
I won’t compare our situations, as no two situations are the same.
But my advice at this point would be to meet him and talk and lay your feelings on the table. Go somewhere you can both easily and safely leave if you need to, and where you can tend to baby’s needs properly.
Before doing so, you need to think long and hard about what you want, and what you think is best for your child.
It is not feasible to pursue a relationship with him if he doesn’t want to be a dad.
Do you want to be with someone who would do callously leave you abs you’re about to birth their son?
What do you want to do in the future? Education/work/housing wise. Do you see him in these plans?
Are you willing to facilitate a relationship with your child’s grandparents without him?
What if he ups and leaves in the future?
See what he has to say for himself. And if you need to, go away and think about it all first before you give him any answers to any questions.