I had to sign up so that I could add a comment from a man's perspective.
Cabrinha sums it up well when she says "its hard work entertaining a child"..... its incredibly hard work and I know as does any responsible parent.
I think those men that walk away from their children generally have issues, BUT it's not just men. My ex wife (I don't understand all your abbreviations yet =)) is useless and would rather be on her phone messaging opposed to engaging with her own children.
Those who are in capable of parenting most likely had incapable parents, I can witness that with he ex's mother (father died many years ago but from what I know wasn't the most capable at dealing with a child)
There are useless men and useless women and all will use the same excuses as to why "the ex" stops them seeing the children and how the world conspires against them. Society also historically made it far more acceptable for men to walk away and a child should be with their mother which is utter rubbish. A child should be with a capable parent or parents if that works.
My daughter was 1 and my son 3 when I ended our relationship and marriage because it was easier without their mother being there and yes I'm a man. I just got on with it for the benefit of both me and my kids, I'm not some super hero I'm the same as anyone else but my upbringing made me realise that I am as capable of raising the kids and so that's what I have done.
Yes it can be hard but you reap the benefits and would you rather go back to having the ex in your life? I think not.
The most important thing is to do what's best for you and the children. I manage my kids expectations because I can as they are still small but never tell them there mum is going to do X Y or Z with them because she usually fails and then they get let down.
I'm happy and healthy as are they and I'm single because my life is about me and my kids and then whoever maybe lucky enough to join our gang one day 
Only ever look forward