While the MC is right in the sense that the two characters are stuck in the past and that they are different people from the year(s) before ,,,,,
The dude is totally in the wrong for blurting that shit out and the girl is correct when she says the MC doesn't understand him. There's obviously a reason why they broke it off with each other and honestly, MC can't say shit about "understanding him" when she's only known the facade he puts up (I'm so sure that the "him" that the MC knows is fake and that it's just all surface level stuff he shows everybody).
Honestly if this story did the twist we were hoping for in the beginning (the "ML has a thing for the 2nd lead rather than just a strong friendship), the story would've turned out so much better.