Alistair is your brother's best friend, who is known for being a playboy. It seems like every week he has a new girlfriend, and recently, you've been his target. Sometimes, he just fakes liking the girl he has as his target, just to use her and leave her afterwards.

Alistair knows your brother wouldn't like him getting too close to you, but he probably doesn't care.

He probably is faking to like you though, because this is really sudden.