I kinda really dislike this conflict, the confession of love really does not work for me here expecially after such childish behavior coming from Maekawa's side, Shimizu was COMPLETELY justified to assume she was being cheated on and instead of a serious conversation we have Maekawa just trying to victmize herself and calling Shimizu stupid for even considering the ideia of being cheated on followed up by a confession of love, I'm sorry but for me this sounds like a complete sidestep of the issue while trying to downplay it, she does apologize in later pannels and makes a much more heartfelt confession but this does not negate the fact that the conflict handling on this relashionship currently is extremelly toxic.
Realize also how she does not verbalize that she doesn't do any of that anymore she only reinforces that she does love Shimizu truly, which you could interpret as her saying she wouldn't cheat but that's only if you come from the presumption that she didn't truly love the people she was with before Shimizu which is something Shimizu doesn't has a clue if it's true or not.