A Potter Thing (слэш)

Severus had always been sensitive to other people's magic. Lily's relaxed him, the Marauders' made the hairs on the back of his neck stand up, and he vomited the one (and only) time he felt the Dark Lord's. But Harry's, the new Defense Professor's, aroused him.
“You’ve been avoided me, Severus Snape.”
“Hardly,” snapped Severus, turning his emotions to anger in a desperate bid to keep the arousal at bay.
“Today, you stared down at your desk while thinking of another man.”
“And how did you even know what I was thinking anyway, you creep!”
Potter pursed those plump and kissable lips of his in apparent annoyance. “That’s certainly no way for you to talk to a professor, Mr. Snape.”
“Oh gods…you look so much like Potter I thought you’d be saved from the Black madness but you’re positively raving.”
“You’re not the only one who feels it, you know,” Potter replied, his voice seeming to drop an octave as he did so. "It’s a Potter thing. From what James has told me, he’s felt the same pull from Lily since the moment he met her. Unfortunately, since she’s a Muggleborn, I suppose she’s not sensitive to it the way you are. Are you done fighting me now? Why deny what is inevitable?"