Yay?
Nay?

But seriously, this topic is about one of the more interesting facets of Seymour's personality that isn't brought up a lot.

What do you think he felt for Yuna?

I don't think anyone would define it as love but he did choose her to be the one to help him achieve his dream of becoming Sin. Even after the party confronts him in Macalania and he drops all pretenses, he says to Yuna "your eyes, they burn with resolve. Beautiful!"