I am going through something similar where children prefer to stay with ex H, but in California the age at which the court listens to what children have to say is 14. At 13, perhaps you can still take your son with you? Or at least split his time and then you would not have to pay so much in child support - the more time you spend with the child, the less support you owe.

You are saying that you have filed for divorce -- does it mean that you have a lawyer to advise you of your rights?