Maybe he recognizes that you are clever, popular, and good at work, so he tries to show that he is too (shows himself, shows others, and maybe shows you too?).
And maybe when he's very nice to others yet cold to you - it's his social way - like he's in control - possibly not really genuinely so nice to them - it's for show. He's showing them how nice he is - is he being manipulative? Is he feeling threatened by them? There is someone who works where I do - and there's this sense of one-up most of the time (anything that I say - this other person will say something to "top" it, and this person seems so nice and understanding with others yet becomes nasty with me in private (others don't see this). I've concluded that this person maybe has a low self-esteem from early on, perhaps it's more noticeable when around someone else who has demonstrated success, and perhaps there are some reasons for this kind of social behaviour.