Jessie and Aeris die, maybe thats why he is reluctant to comit to Tifa, in fear of her death. maybe he thinks he's cursed, Then again he does hug Yuffie, and she hasn't died, but she seems to have gone off him in favor of a more emo-tastic hottie.
Oh and Zack, he was well fond of him as well and he died. he must be cursed