I agree with Starry, my DD is now 17, she's not met her father. He made it clear that he wasn't interested as soon as he knew I was pregnant.
I've always been honest, in an age appropriate way, with her.
I've not really said anything against him, she can make her own mind up about that, but started off by saying he was really busy etc if and when she asked why she didn't know him.
When she was 12, she had a short phase of wanting to meet him. I did what I could, sent a letter to his parents address, but no response. When chatting about it a few years ago, she said that she realised how loved she is (my whole family have been great) and it doesn't really matter, but she is curious. Maybe she'll take matters into her own hands one day.
What I really want to tell you is enjoy your son, you don't have to share him with anyone and you can bring him up just the way you want to. Have an honest and open relationship, where no topic, including his dad, is out of bounds and everything will be fine.
I understand your frustration, how can he not love your amazing son? I have no answers to that.
Sorry for the long post, I wish you both happiness.