Me and my ex girlfriend have a son together and they lived in my house for the whole 2010 she is now moving out and she done her taxes already claiming my son is that right or is there something I can do to claim him

I suppose there is no chance of simply negotiating with the girl friend to determine who gets the most benefit.

Therefore, if you can PROVE that you provided more than HALF of the child's total support, you can claim the child as well and, when the IRS challenges BOTH returns to sort out who get to claim the child, you SHOULD persevere.

However, if your girl friend filed as SINGLE, YOU can file as HEAD OF HOUSEHOLD even if youdo not claim the child. This allows yo some tax benefits as well.