So I'm guessing that she wanted to date MC, but thought he was taking too long, so her plan was to pretend date that other guy and break up with him not long after so as to pressure him into confessing, which obvs backfired.
The actor guy either actually hates him because he's her childhood friend with feelings for her, which means he could have lied and became an actor because he wanted to be more like the guy she liked, OR he genuinely just wants him to act again, and faked hating him in order to goad him into doing this whole thing like MoonStoneX said.