Loveless by Yun Kouga

Catboy angst.
At the age of 10, Ritsuka lost his memory. His entire personality changed, causing his mother to go crazy and accuse him of not being her son. For a while, Ritsuka's older brother Seimei protected him, but then (one week after revealing his true name to his brother) Seimei was murdered and left in Ritsuka's desk at the elementary school. Two years later, Ritsuka is still going to counseling every week, and he is abused daily by his insane mother. One day he is approached by an attractive college student, Soubi, who claims to have been a friend of Seimei's. Thrilled, Ritsuka immediately agrees to spend time with him. When they are attacked by another pair of children from the organization that killed Seimei. Soubi reveals that he is a "war machine" who had been Seimei's partner and is now Ritsuka's partner. Ritsuka is desperate to know what is going on, why his brother was murdered, who these people in the "Seven Moons" organization are, and most of all whether Soubi really cares about him.

BL manga for sale at Mangaroo.