Disclaimer: I don't own the characters.
Draco knows it's wrong. It's wrong and it's bad and he knows his father would have something to say about these fantasies, because real men don't dream about other men touching them and loving them. They don't dream about being loved at all, but being feared, being worshipped, being adored and having control, and it's always by women, because women are weak and men are strong. That's what his father would say. And he's always listened to his father because Lucius Malfoy knows what he's talking about, and he understands the way the world works, and no one else can advise him as well as his father can. He knows this.
He also knows that he can't control these feelings. He tried telling himself at first, back in the beginning, when it all started - has it only been four years? It feels like his whole life - that it was just a crush. A little schoolboy crush on his teacher, because Snape is strict and firm and cold and cruel and everything Draco wants to be. Snape is a real man, like his father, and Draco used to tell himself that he was just looking for a replacement father figure while he was away at school, that was all.
He figured he'd get over it. He'd stop being an immature child and start realising that his admiration for Snape as a person and a teacher didn't have to be so all-consuming. It wasn't anything more than that, it's just a little bit of a crush, it doesn't mean anything, it's perfectly natural. Because actually being attracted to him - well, that wouldn't be. He'd never be able to show his face again. His family would disown him. He couldn't admit it to himself, because then it would become real. Then it would become something, take form, have an identity, instead of being a shapeless thought wandering around at the back of his mind. Always there, even when he doesn't realise it, Snape is always in his mind. Sometimes he's just there, not moving, just there. Other times he does move, but Draco doesn't let himself think about that too much. Not often, anyway. At night, sometimes, when everyone else's asleep and he knows no one can hear him, and he lets the fantasy play itself out, and Snape's grabbing him and touching him and stroking him and sucking him and it's hot and sticky and sweaty and it's gentle and it's rough and he's never felt this good before. He comes calling Snape's name, but softly, because he's still afraid of being caught, of someone knowing what really goes on in his mind.
In potions class he can't help but stare. He doesn't let himself think about the fantasies in that class, either, because then - well, then he might just give himself away, say or do something that would let everyone know, including Snape, just what Draco Malfoy wants and dreams about. His friends know he looks up to Snape, he can get away with the staring for the moment, but anything else - no, he knows that the second he crosses the line, the second everyone realises that Draco isn't a real man, not like his father at all, his life is over.
He keeps it to himself, and when he feels Snape's hand on his back as he looks over his shoulder to check on his potion, he bites down on his lip and hopes no one notices how precious that touch is to him.