TLDR MC never took serious the feelings from his CHF, then came the other guy who took advantage of her broken heart and got into her panties, MC heard it all from another room and ran away crying. To the other guy CHF was just another target for capture to brag about to his friends.
This NTR doesn't really make me feel as bad as much.... The MC is so much of a pathetic braindead idiot that you don't feel that bad about him getting cucked at all!
The most heart-wrenching crushing NTRs are the ones that either isn't directly the MC's fault, or the MC was just not quick enough. The more it feels 'avoidable', the more heart-wrenching it feels. But this fucker here brought on his own doom with the way he turned her away multiple times even though she was practically throwing herself at him. This kind of an idiot deserves to get fucking cucked.