One of the best things about being with someone, is that if you do it right. You'll never know them completely. You'll always learn something new about them for the rest of your life.
Good or bad. Happy or sad. Learning the truths about someone isn't always a sunshine moment, but it is an intimate one nonetheless. The fact that the person let's down their guard enough for you to come in. That you've earned their trust that much that they'll let you hurt them (not that you would).
That's a beautiful thing.
Learn, everyday from that beautiful person you're with. And take a moment to recognize it. You'll appreciate your station in life a whole lot more.