Unable to Handle Immature Partner

For some magical reason, it just NOW dawned on me that I have conceived with a completely immature person. The baby is due in a matter of 4 weeks possibly less and I can’t handle being in relationship with the baby’s father anymore. He and I might be able to get on the same page for our kid, but relationally for a life long partner, I’m 90% sure I screwed up and chose wrong. I’m feeling there’s not much to do now. I want him in his kid’s life and I want him in mine but it’s simply not working relationally. I clearly was blinded and tremendously wrong when I assumed a (partner and father of baby) 22 year old would be able to rise to the occasion and actually put effort into a real adult relationship, with a mature almost 27 year old (me). Insight is needed because I want what’s best for my child and I.