Man that was disappointing. Anti-climatic and artificially created drama.
Let's just imagine for a second he is older by 1 year. Basically meaning at every point in her life, there was at least one year where they weren't together. (Elementary school, junior high, high school)
Him being dominated by a girl for 10 years? Hardly believable, especially when they were younger, children are very elitist (age) especially during the younger phases where difference in one year is huge.
Next biggest disappointment is conversation about love. "I think she liked/loved you" <- Nope, she wasn't what MC said in chapter 29 was correct. She didn't love him, she loved herself and liked having a secret trophy boyfriend. When she noticed that he was charming (i think other girls noticed this first) she decided to make his good features disappear.
In any case her actions were akin to sociopath's/psychopaths/narcissists, these people are not capable of feeling empathy or love. They can be possessive but love isn't something reachable for them.