You don't have to be a cuckold.
I totally understand that you would want to stay around for your ....... Mum's enjoy the lions share of rights and say post divorce. Anecdotal accounts would seem to imply that children from broken homes can have issues as a result. If I could be bothered to google I imagine there are studies that would back that up.
But you can make a new life if you want to. Would it be that great for him to grow up knowing that his mum has no respect for his dad? His mum doesn't love his dad?
I feel for you, it's not a nice choice to have to make. Maybe you could explain this to your wife?