I truly hope the author is not trying to pull some redemption arc bullshit here...
And how the hell can this cesspool of a human being say that "she loves him", in the very first chapter we see her tormenting and abusing the MC on a daily basis for years, and even seen her having him stand out in the rain for a full hours until he had to be hospitalized, for no other reason other than to humiliate the MC and prove to her friends that he would do as ordered.(her male friends btw...so you don't get it out of my head that she has cheated on the MC, if for no other reason than to prove that she can).
Honestly if this is not the point where the MC brings up a nice highlight reel of her abuse and how she literally got him hospitalized, then tell her to leave him alone for good and make it VERY clear that no matter what she does, and how desperate and lonely she tries to make him, he will NEVER be together again with her even if all of humanity were to be extinct then and there and it was up to the two of them to repopulate the planet.
In short this is the part where he has to "spew venom" and be as clear harsh and untactful as can be, in order to make his position clear....any half measures will only end up with her still retaining hope that they'll get back together.