Schlatt was a hitman he shot first asked questions later, he didn't ask why he was taking somebody out as long as he was paired he'd do it. You were dating Schlatt, he loved you dearly and would protect you with his life so when he heard your previous partner was abusive he saw red he wanted you to tell him everything but you only gave him a name... He could work with that. He searched high and low and found your exe killing him brutally (of course) bringing his head to you