Well...maybe because in the two pages that we saw him, he was kind of a jerk....?
Not knowing his story is not an excuse for being a jerk. That's how in many other yaois we excuse the maltreatment or rape of the uke....because "we don't know his story yet..." (seme's)
KEKE, DO YOU LOVE ME? ARE YOU RIDING? SAY YOU'LL NEVER EVER LEAVE FROM BESIDE ME