@KamiKira00 "I don't understand why MC keeps pink haired girl as his wife. " I don't think he might not have a choice there. He isn't the strongest and each one of those "elders" are more powerful than him. He's probably stuck with her until he reaches the point where he can overpower entire sect by himself.
"author writes as if past doesn't exist." He actually doesn't write this way, as he spent 50 chapters with that "Eunuch" thing. Also, regarding the pink haired girl. One could think about it this way: imagine that you ran into a monster in the forest, and said monster tried to eat you alive, because that's what this monster does. Then by application of wit and luck you managed to convince the monster that you're more than food, and you started talking and hit it off. Because when that thing no longer sees you as a walking hamburger, you could talk to it, and realized that it is actually intelligent and has things to say. Something like that. In position of slave, MC was pretty much a human dil... I mean battery to the "pink-haired girL", meaning a thing that needs to be drained and discarded. Learning the cheat abilities allowed him to show that there's more to him, and hence possibility of being treated as more of a person.