He is there when you are sad. He doesn’t run for the hills when things get tough for you. He stays, and he supports. He knows that not everything can be perfect all the time.
He doesn’t back down when you are mad at him or you just had a fight. He always does his best to talk things through and solve all the issues you might have.
If he realizes that he was wrong, he will apologize without a problem and do his best not to repeat something that has hurt you.