Sephiroth wouldn't say so (just yet) but he'd be very grateful for Vincent treating him like a person rather than the 'similar-to-a-bomb-ready-to-explode-any-day' treatment that he can't help but perceive through Tifa and Yuffie no matter how the former's point of view may be starting to change.

Not to mention Aerith but the CR hasn't got off the ground yet...I'm not sure how well he'll deal with living with the girl he comes to kill later for getting in his way/larger revenge for his Mother. Especially now he's just lost the one person he could have talked to about stuff but never did due to his own pride.

And yessssss, I love this idea of Vincent-helping-Sephiroth-to-be-happy partly as a way to make it up to Lu and partly to prevent another going through his pain.