Jamie Milkovich is the brother of Mandy and Mickey and son Terry Milkovich. He appears in season one when Ian rejects Mandy's sexual advances causing her to send her brothers after him in revenge. Jamie is one of the three brothers who try and hunt Ian down in this episode (the others being Mickey and Joey Milkovich).
Jamie does not appear after the events of "Aunt Ginger". However, in Can I Have a Mother, one of Mickey's brothers states that all the drugs were used up at a quincenera at Jamie's a week prior, implying that Jamie has, at this point, moved out of the Milkovich house.