I am single mother and have a 18 year old as of last August. He is still a high school student. It is my year to claim him as stated in my divorse.
Can I do so?
Also he earned right at $2,800 and only paid in Federal $100 SS $170 Med $40
Does he have to file separatly?
If he does do I still claim him?

Yes, you can claim him if he lived with you and did not provide more than half of his own support.

He is not required to file but he should file return to get refund of $100 federal income tax withheld. He will not claim his own exemption on his tax return. Your U.S. Tax Return: Filing Requirement for a Dependent (http://taxipay.blogspot.com/2008/02/filing-requirement-for-dependent.html)