It is a little too late for that realisation, he can not undo what is already done. Though he is in denial he has already caught feelings for Jules. Is he willing to let her go to be with Damon? I do not think so.
Hmm…Damon is headed in the right direction. Getting real information about her is a great next step. Maybe not relying on his normal sources but personally chosing an outsider perspective. Additionally, it would be best to talk to her more to make up his own mind about her.