I think this is your ego that is envious that your ex can lead his life carefree, whereas you have your son and two job bs that keeps you busy.
Could I be right to think that you still think that what happened to you was/is unfair? I'm not asking this to make you feel bad. It's more that when I read what you wrote I feel the same and I believe that in my case I want my ex to feel what I felt and that I feel like life is unfair as ex gets away with murder.
All I can say (and it's easier said than done) is that it's in the past. You are poisoning yourself by overthinking and being "envious" of what ex's life could be.
In our cases exes are like who they are and unless they do the work on them (and realise what the causes are for them to behave the way they are) and decide to change by themselves it's something out of our control. So there is nothing you can do.
Men and women aren't geared the same way. There are some men out there who are great fathers and emotionally stable, and there are other who behave like kids and put themselves and their needs before their own children. Those people have some childhood issues to solve but we can't solve them for them. They need to face whatever has happened in their childhood and to deal with it once for all. However it does take courage to look at something one doesn't like and not many people are prepared to do that so they prefer to run.
For NG I would say follow your gut feeling. How do you feel when you think about him? How is your body language when you are with him? Is your body tensed or relaxed?
I hope I'm not out of line but are you with him for the right reasons or are you scared to be on your own for the rest of your life? So you have decided to settle for less than you deserve.
For me I have noticed that having expectations always create disappointment, so I try not to have any and try to live in the present.
