Marriage as forgiveness school

I think that Martin Luther should have kept marriage as a sacrament. Why?

Nothing has ever helped me understand the nature of God's love better than my marriage (except, perhaps, the love of my parents for me). I am always amazed and grateful when my husband forgives me for the boneheaded things I do. I'm even more amazed that he's often forgiving me for making the same mistakes again and again.

These are not major mistakes. I don't go out and cheat on him, for example. But I'm often irritated and grumpy, and I lash out, and I realize I've been a jerk, so I apologize and ask for forgiveness. And he kisses me and says, "Don't worry about it." And again and again, I feel blessed with a kind of marital grace.