Confused

(California)

My ex and I divorced in 1993, in the state of California there was no child support ordered, she lived in Texas I lived in Wyoming and 1/2 in California. My son did come visit for a few weeks in the summer when he was younger. I have not seen him since 2000 and he will be 18 on May 7th. They disappeared for three years, apparently they were in Europe. She has always been able to get in contact with me. I have just recently been in contact with him mainly via email and we are starting to build a relationship. The ex is now threatening to take me to court for back child support that was never ordered unless I agree to pay her $500 a month for the next four years. I feel I should pay something but do not have $500 a month to give and feel that I should probably go through the courts or she will pop up and down the road demanding more money. She now lives in Washington, my question is does anybody know which state has jurisdiction? I went to see an attorney and he thinks it is California, but the County Clerk thinks it would be Washington if they have lived there more then 6 months which they have.