A friend is writing a book about me?

It sounds like he's had interest in you for awhile. Often times I base characters on people I know, adding quirks and nuances of their personalities to make them seem more realistic. There have been scenarios, however, when a character is entirely based on a person I know, so it's quite possible that is what he's doing. And generally, yes, the way I write about them (if they're the enemy, love interest, or the likable sidekick) does reflect how I feel about them in real life.