the seme was NOT a victim of any abuse, it was his little brother who his biological parents abandoned him and then the seme parents didn't care for him. the seme was the one who raised the uke. while he raised him he showed the firsts signs of a classic sociopath personality and abused him mentally/emotionally. for many sociopaths is normal to not form bonds with friends. and their lack of conscience don't allow them distinguish from right and wrong. the mangaka portrayed the first steps of a serial rapist/killer very well.
Read Mitasareru Kuchibiru, http://www.mangago.me/read-manga/mitasareru_kuchibiru/ before ya'll start ragging on this story squawking about "Glorifying Abuse". This type of situation is more common then you might think and the portrayal is quite realistic. The seme was a victim of a form of child abuse for his entire life and had no friends or adult guidance to help sort out the difference between right and wrong. Not agreeing with his behavior at all but I was able to understand him a lot better.