It's honestly baffling that MC was this amiable with her after her reason came out. A girl rejects his confession because "It didn't feel like the right time" with a made up reason that is sure to break his heart ("I have a boyfriend") and gets jealous and clingy when he start to seem like showing interest in other women because, I dunno, she goddamn broke his heart?!
Like sure, he was pretty mature in not forgiving her in a calm manner, but I have no idea why he's still interested. She's clearly shown she's capable of lying when it suits her and being manipulative, not exactly qualities you'd want to see in a significant other.
Think about it if the genders were switched. It wouldn't be treated the same like in this chapter.