Well, he’s taught in schools as an archetypal unreliable narrator, so it’s impossible to be sure, but he’s kinda shitty to date - he supposedly has a girlfriend? fiancee? somewhere in the midwest he sometimes writes (but maybe not) while fooling around with Jordan (and maybe another girl in his office). Not that big a deal now, but I was under the impression it would have been more scandalous back in the day.
But my biggest hitch with his character is that he watches all the terrible behavior around him and does nothing. He’s a confidant that people tell their secrets to, but he just kinda… sits there. Hell, up until the very end he could have been a figment of Gatsby’s imagination the whole time.