now it seems that the only reason he sided with Luke instead of Asch is because Asch is his enemy's real son. =_=

I don't see it that way, though. :) Like Guy said, he doesn't care much about the revenge anymore and Luke's the one he grow up with the most so he would rather be with him. I'm sure he already warmed up with Asch before Asch got kidnapped. It's just that he prefers Luke because he has spent the most time with him.

Eeh, my 2 cents, anyway. As a yaoi fangirl, another reason I think Guy stayed beside Luke is because he's in love with him, hahahah. 8DDD