Ah, did you read the raws too? Doesn't seem like she forced him to be with her. Maybe he forgot about Lin Yin or the promise or thought that there was no need to fulfil a childhood promise, and went and be with another girl instead. If he really wanted to be with Lin Yin then he needed to break up with his girlfriend. But the manhua's main couple seemed to be Lin Fan x Lin Yin, so there is no hope for Xing Yu x Lin Yin. Ah well, that guy is a scum after all so he doesn't deserve Lin Yin.