I don't think he's like that just around you. He's just known you well enough to show his true colors. When some one shows you their true colors, believe them. I've known many people like this. I've fallen for their surface presentations of themselves. In falling for that, I ended up letting my wife date a guy like you've discribed whom treated my wife like **** and is the sole reason my wife is now my ex-wife, and the sole reason she is utterly convinced anyone who claims to love her lies through their teeth and cannot be trusted. Why people are like that? I don't know. But after the guy that cost me my wife/my best friend..... I've learned to be more careful about who I let in my life and whom I share with.
People differ. While we all do "impression management", some are more honest in what they present. Some people reveal themselves quite easily and quickly, others only show their true selves much later.I have a preference for the former type.