Remus smiled.
That was it. No thundering revelations, no skies opening, no terrifying moments of clarity-no it was just a smile. One smile and Sirius could tell he was in love. But to be fair, it was a beautiful smile.
It shouldn't have been, but it was. You really know its love when someone looks…well, rough is the only way to put it, and they can still make you weak at the knees. When they've been crying, and they've got puffy eyes and snot running down their face, and they still make the bottom of your stomach drop out. It's got to be love. Or really big trouble.