I think not willing to let you share on his FB is a very telling thing.

How old is this guy? Is he an older bachelor? Ever been married or in a successful relationship? Does he have a pet, that he loves? Does he treat service people in public in a shabby way? Like waitresses or salespeople? People who do that are self centered and selfish. Does he complain alot about how he is "treated" in some situations? Does he hate waiting in lines for service? You obviously see him in real life, so you would have seen how he treats others.

I have found that men who remain bachelors, and never commit to a relationship have odd behaviors, and "reasons" for being so.
Some men are VERY self centered. The more so, the worse for any female in their lives! If he is a narcissist, you'd best beware and avoid any entanglements, beyond the superficial.

I personally think that too much teasing (as in the older brother stuff), can become rather revealing of a hostile personality. Some teasing can be fun, but lots of teasing becomes demeaning to the victim and reveals a bit of sadistic pleasure in the giver. Young people tease alot these days...and I know my son, who is rather sensitive never never liked it! It sets up a gradient of the victim being "less" than the teaser ...who needs to feel superior. When it is done in excess, as a major communication tool, it reflects immature and selfish attitudes IMO.