What's the unquestionable proof that someone loves you?

I think that if someone truly loves me, then he/she would care about the people and things and animals that I care about. And that he/she would respect those most important to me and will protect what I would give my life to protect.

It's a simple determining factor. But somehow, I realized that failing it makes me question one's motive for getting close with me. Because to be honest, if I love someone, then I like to think I'd care about these things about him/her too. Or at least, that's what I hope.