I’m also saying FMC should be criticized as well
Criticized for what? Things that were obviously evil, that were (and continue to be, in fact) already criticized and are no longer happening? Why beat the dead horse over completed actions, in tandem with continuously criticizing ongoing actions? Why even bother, when this guy is more than willing to repeatedly insert his own body into the body of this woman that sexually violated him?
My other point is that while its a bad action of MCs it makes sense for his character.
It makes sense for his character if we're supposed to view him as a hypocrite and snake who thinks he's entitled to doing whatever he wants to other people because he was hurt.
Again, I'm not concerned about whether he forgives her or not-- my consternation is that he pretended to and then formed a relationship with his former bully under false pretenses. A relationship where she opted to actively do things for his sake, including giving over her body for his sexual gratification and using herself as a lightning rod for his bullying. He can just
not forgive her and not have anything to do with her-- or, he could have not forgiven her and then joined with her bullies to begin with.
She emotionally blackmailed him
No, she didn't. She
regular blackmailed him, and also ran the regular gamut of Japanese bullying. They weren't in an intimate relationship prior to or during her bullying campaign. He doesn't recount any
betrayal from her. She doesn't recount her doing anything like what he's done to her. What he is doing was a novelty in their interactions by the start of this narrative.
Which makes it a bit worse-- because, of course, it'd be ideal to think "if I think what happened to me is bad, why do I want to do that bad thing to this person". But he didn't start out doing something to her, that she did to him in the past.