Remus nodded. He probably shouldn't have said anything. Silence was probably best for both of them, but he sort of felt he owed it to Severus to be a little more than civil to him. After trying to kill him (inadvertantly), and knowing Severus knew more about him than most and had to be trusted to keep that knowledge a secret, Remus didn't think it'd do him any favors to be impolite.
"Yes, them," he said. "Things haven't been right since the Valentine's Day Ball. Something happened, and it's been.. very trying for all of us ever since." He knew he was being vague, but it wasn't as if any of this was easy. Snape wasn't exactly the posterchild of warmth and compassion. He also didn't think Sirius would appreciate him spilling his situation to his mortal enemy. Though, really, Remus would be surprised if Severus didn't know what he was talking about, being in Slytherin and all.