Yes, it's been suggested that Charley is in love with Frank, and it's possible, and it's certainly something an actor can play, but I think it may have more to do with the fact that it was Frank who made Charley aware of what art is capable of achieving (or at least what Frank at one time believed art is capable of achieving, and Charley continues to believe it).
It's also true that if you believe that someone is tremendously talented, as a bunch of people believe about Frank, then you are probably going to continue to believe that the person is a great talent, even if you believe the person has abused his talent.
But clearly Charley is not all right and Frank is not all wrong. I love a line of Mary's that got cut even before the opening in 1981: "Hail, Charley, full of grace," in response to some of Charley's self-righteous lines.
Which brings me back to wishing that if Sondheim and Furth felt so strongly about revising the show, they should have restored some terrific stuff that got lost along the way to opening night.