Nah, getting sex through guilt tripping and emotional manipulation is rape,
It is
not. Let's not undermine what rape is-- this doesn't have to be rape in order for it to be awful. In fact, it would (logically, at least) be a point-of-no-return condition if it were.
He wasn't physically constrained, incapacitated, unconscious, mentally disabled, or even blackmailed. She has no position of power over him. Neither of them are children (or, rather, they're legally allowed to have sex with each other). She doesn't even have real leverage over him-- this relationship is not directly or indirectly necessary for this guy's life. He could have as well have threatened to break up with her instead of acquiescing to her new terms for the relationship/giving into her emotional manipulation-- and calling her bluff and squarely rebuking her in the last hapter might have had her apologizing like this back then.
Trying to cast this as rape distracts from what actually happened. What she did was bad because she unfairly called into question his attraction/care for her-- while banking on it to be real, paradoxically-- in order to get shallow validation at the cost of compromising (and getting him to compromise) his virtues despite her willingly going out with this guy who doesn't want to have sex right away. It's a nasty impugning of his feelings for her despite the fact that she knows very well that she started this relationship just because she wanted to have sex for having sex's sake. It's excessive because all she has to say is what she now feels-- she went through that manipulation
just to avoid saying she liked him. She even compromised her own resolve to get him to like her
without seducing him.
...or maybe the mangaka just wanted an almost sex scene, I dunno.