"I don't think I'll love anyone else but her... for the rest of my life"
Ah, youth. Such an innocent line. It sounds like something that someone of his age who's actually deeply in love would say. This boy really is pure-hearted, isn't he?
That must have stung to hear for Sugiura, but I suppose that's just the consequence of pushing further when he already rejected her. She had her chance to leave before getting herself hurt even more, but she just had to push her luck.