I just wanted to chime in with a personal story - well, a friend's. Her "sperm donor" flew the coop and has been paying scant CS for about 5 years. He was young and they weren't together long. Last time he saw their kid he was 18 months old, and before that only a few times. Always awkward, even the letters he sent, which were very few. Didn't know the first thing about kids - that was obvious.
Well, he's now a ripe old 26 years old and in law school. He recently let my friend know he is trying to get transferred to a college nearby to her so he can be near their son. While he works on that, he is going to visit. Last week he came to town just to see their son. He and their boy spent the whole day together and had a great time. A bit emotional, understandably, for their son, but what my friend learned is that no matter how she feels about him, she sees how important he is to her son (of course, right? That's DAD). And she sees her "ex" is growing up. He may even be reading some early childhood development stuff to get up to speed, since he seemed to have more of a clue of how to relate. Or maybe he does better with 5 year olds. Who knows.
But I wanted to say that it's been hard for my friend because she's human and she's protective and part of her feels resentment toward the dad that he got to keep partying and living "the life" and she had to be oh so serious and dedicated and broke, and, well, a mom. But she doesn't act on that stuff - she acts on forgiveness and facilitating a relationship with the father. I have learned a lot from her and quite frankly from this forum. It can feel a certain way (unfair) and it can in fact be a certain way (unfair) and we STILL have to keep in mind that our children just want to know their parents. All that legal stuff still needs to be addressed behind the scenes, but we also need to spend time thinking like our children and remembering how important parents are to them, even with all our defects. And we never know what the future may hold. People do grow up and man up, but maybe not on our schedule. It's probably too late for my STBX who is pushing 60, but i wouldn't be so quick to pass judgment on someone younger, and I would assume your baby daddy fits into that category.
The advice here is harsh but does often help get your head screwed on straighter.