Disclaimer: Harry Potter isn't mine.
Severus' POV
You thought you'd never have to see him again. Unfortunately, he lives at Order headquarters with his deranged mutt, whose home it is. When you first came to the new headquarters, you expected Lupin to be happy together with the man he chose over you. But he wasn't; he was miserable, and they weren't together. It gave you a vicious kind of pleasure to see how low Remus had sunk. Playing nursemaid and housekeeper to a dipsomaniac had aged him. There was far more grey in his hair than before, and every time you saw him, he was exhausted. Eventually, far later than you should have, you realized that he was watching you. The pleading look in his eyes would have melted your heart once, back when your heart wasn't buried under a glacier. A glacier he put there, you remind yourself. He's already betrayed you once; he could easily do it again. You wouldn't dare take him back, even if you wanted to. Your sadistic side, your only side now, relishes his attempts to get you alone, and to apologize. You always cut him off, or pretend he doesn't exist. Every time it happens, his shoulders slump a little more. Let him despair. It's no more than he deserves.