The term a good dad refers to many aspects. Being uncle dad, a good laugh and as you say arsing about, is good in some respects, but bloody awful in others.
Then there is the way he treats women. The way he has treated YOU.
Basically if your H doesn't grow up and show that he can be a decent dad, a good man and a great H, then how is your DS going to learn. Would you be happy knowing your son will grow up to be exactly like his dad? to cheat on the mother of your grandchildren, to never pull his weight?
You being happy, respected, fulfilled and not cheated on will teach your DS way more than you sticking this existence out. every trip home you will wonder how many women he is screwing. Every phone call, text, email.
Imagine this. You leave this wastrel. you come home, you restart the life you were well on the way to leading before mr snake diverted your attention. In time you may meet someone who DOES live a decent life, who IS a good amn, father, husband. Perhaps he has great parents that can provide you with help. Perhaps it'll spur your parents into helping.
The reason they don't help may be due to how they feel about your H.
My mum has let me down so badly with my 'H' going, she still won't talk about it, it's all brushed under the carpet and I am left recovering on my own. Oh yeah right, she'll collect DS if I'm working, she'll invite me over, but will she ask me how I am? No. Lately she seems to even try to limit contact, not listening, trying to end a phone call, I feel utterly abandoned by her, when I was the one that stepped up to help her when Dad left. I was 16.
XH is in Egypt, DS doesn't really want to talk to him. Not entirely sure why, but as H never did anything, DS knows the only person to go to in any hour of need is me. Now he has a happier mummy all to himself.
Don't let your DS be a reason to stay in a marriage where you are not truly valued. Please go and read WWIFN recent post on why she and her H got through his affair.
Please don't let some egghead come up with a document to keep you trapped in a life to nowhere.
You have to put your family first, and your family starts with YOU, your son, and then a long, long LONG way down the line, the bloke who chose to betray you.
Remember, nothing is cast in stone. The FEAR of suffering is worse than the suffering itself. The fear can last a life time, once you have ripped off the proverbial plaster, the pain can only last for so long.
Fuerza!