It is horrible
Yup! But I don't think this could have ended well, in any case since the other potential lover just watched it happen without doing anything. In my ideal situation, he would have just avoided both of them altogether and found somebody else to love.
I do think the trope of ending up with someone out of pity and watching that grow into love is unexplored in yaoi, so I liked the concept, just wished it didn't start with rape. I could deal with a punch or two, or even attempted sexual assault on a very conscious and capable uke. But drugging someone and then raping them? There are just too many instances in that where you have to commit to being evil.
Im always bothered by anything that has to do with rape. Yaoi mangaka end up romantasizing it so much that its just become the norm. But i feel like i have to remind people that rape is bad in every way possible. If the victim falls in love with their rapist its not "cute" its not, in any way, pleasing. It means the victim has a psychological disorder similar to Stolkholm Syndrome where you become tramatically bonded to the rapist. Therefore, i do not like any manga that features a rape scene. It's horrible.