I too am sorry to hear of your plight having been through over 10 years of problems relating to contact with my daughter.
In my experience you will more than often come out 2nd best in any disagreement with your ex, it is not fair or just but there is not a lot you can do about it.
For what its worth my advice would be:
Maintain your dignity and don't argue with your ex, especially in front of your son. Just walk away.
Avoid the CSA at all cost. (Before anyone says anything I don't mean don't financially support your child, just don't let the CSA get involved.) Pay by standing order or some way you can prove what you pay.
Whatever you do maintain contact with your son, at times it will be hard but believe me when he gets older he will appreciate you more!
Good luck, you're not the first and you won't be the last.
