N and children?

One of the most confusing and difficult part of me I healing is my relationship with the N and his child (3years). Like a normal relationship the N waited to introduce me to his child. I was so honored when he did. In hindsight I remember him saying odd things like he doesn't like anyone but me (I dismissed it as being protective and asked why he wouldn't want him to like me as well).
Regardless me and the child grew close...breakfast swimming playground I spend a lot time with the child and N and it began to feel like a little family. This really lead me to believe that our relationship was serious because why would someone Introduce me to their child especially when the child can talk and tell others. I have a lot of male friends, Divorced and married and One thing they all say is that they never introduce their Children to any women unless it's very very serious. My N works a lot so he only had a few hours a day with his son, but it seemed like the time he had he was such a loving father the times I saw him. This is one of the biggest reasons I fell in love...we bonded over me raising my son and him raising his son. One thing that struck me was sometimes his son seemed very timid and scared he was 3 while my son who is 2 was way more talkative and a daredevil (also dismissed as personality).
When it all exploded (the mother of his child called me) said he is a horrible father. When she had a c section he left her at the hospital and went shopping and lied and said he went to work. That he was never around, never held his child as a baby. She almost laughed when I asked is he a good father. Instead She said he is a liar and lies about everything.
Now I am left wondering what I just got hit with. Do N use their children?? Do any of you have experience with this. Was this all an act? Even though I saw him being a wonderful father is it an act?
Somehow its inconceivable to me that he used his child to use me and my child and it sends me into serious denial. Please help ladies....