When he loves you, even during the times he doesn't like you.
When you are sick and you're in your bathrobe and your hair's in snarls and you haven't washed your face in 3 days and he looks at you and the word "gorgeous" comes to his lips.
When he refuses to take the easy way out and leave during an argument, choosing to stay and hash things out because he'd rather be with you during the bad times than with anybody else during the good times.
It's called unconditional love, and once you're lucky enough to find it, hold onto it.