Gave a check to the raws.
MC was able to have sex with his crush first, but they both virgins and so she suffered from it, MC didn't had the skills and this girl is weird in the head because she clearly loves him.
I think the "many shapes of love" thing is because she got used to seeing MC father with multiple bitches, so in her mind a multi parnter relationship isn't that abnormal, she knows is weird for normal people, but for being exposed to it from a long time she doesn't refuses it, when she had the first sex with MC his father did stimulate her sexually before, even pissing MC off when he showed her naked overstimulated body to him, gloating, he got punched for that.
MC is not a pussy, he loves the girl and wants them to be together, but she is broken in the head.
There is a flashback to a funeral and at a certain point she looks to MC father with admireation, I think that she got infatuated with him then, and probably the funeral was for her family, the father possibly helped her, creating a incredible debt, that she decided to repay by becoming another hole.
After that it seems like MC starts to fuck his father bitches and gets more skilled, and then when doing a foreign girl introduced by one of them the crush enters the room, the father seems to have planned the event to break their relationship as it made it look as MC would have sex with anyone.
Is raws and I can't read them but the relationship is shaken for a bit, MC still fucks the girls, possibly stealing them away as they loved his father but realized he is a asshole, his father finally confronts MC after he had good sex with the crush, the 2 have a big vocal clash and in the end the father keels over, seems like the stress finally made his age catch up, but the way he entered the room it wa sweird after the previous part with him, maybe the wives had cut contacts and he got angry at MC, accusing him of ruining his harem, or mayeb it was because MC and crush were able to pass the wall he had created and got togehter anyway.
The father did have sex with the crush, but it was very hard, he treated her mostly as object for his own pleasure, when MC did it with love and care.
The finale was pretty weird, after the father is recovered he seems to calm down and have a decent talk with MC and crush, finally let them be together, his harem arrives to care for him, with another young girl that is introduced as the 5th wife, she resembles crush a bit but with black hair, so yeah, don't cry for the asshole, I think the harem isolated him to make him care for them, to make him understand they aren't just walking holes.
No member of the anime kills themselves nor drugs are ever used, maybe when the father gone to MC all angry he had drank something, but is not shown, the only harmful to the body vice showed in the story is his smoking.
The last pages show MC and crush together, happy and with a kid, we never see the girls parents so I think that the funeral theory is correct.
I rushed through the raws, they were old and low quality and I can only assume the plot, but some things were fairly easy to understand.
Long post but should answer the questions of most unlucky souls that found this serie, I hate NTR, I hate stupidity fueling the NTR, but I even hate not knowing how a serie ends, hence this effort.