URGENT HELP NEEDED

My name is Della. I live in Washington County, Portland Oregon. My ex husband Jason Richmond lives in Clarkston Washington.
After 8 years, Jason has come back into Tiylurs life and just now started paying childsupport. Now, Ty spends all but maybe 2 weeks of the year with me. I have custody of him. Jason is saying that he has talked to a professional and that person told him that legally he has the right to claim Tiylur on his taxes even though I am the one that Ty lives with most of the year and my current husband currently claims him on his taxes at work. Jason also owes almost 10 grand in back support and currently pays 250 dollars a month which only started this month. Before now, he was paying 85 dollars and has only been paying that for the last few months. Jason until now, wanted and had NOTHING to do with my son.
I'm wondering how this all works and what my rights are as far as taxes. Last thing I want is to find out afterwards and end up owing taxes or something. I just don't see how after 8 years, he can just pop back in and take over like this.
Thanks

For information regarding your rights on claiming your dependent (child) in your income tax you must refer to the income tax forms of every year on the section about the rules of claiming dependents. you will find out that a child can be claimed as a dependent for tax porpouses by the parent that provided more than 50% of his/her expenses during the tax year claimed.
for more information go to the IRS web site.