Don't think about him. Don't. You know you shouldn't. You know that teacher/student relationships are forbidden. You know that thinking this way is wrong. He can't be any more than fifteen years of age. You're old enough to be his father. Hell, you know his father, which makes it even worse. If Lucius knew the way you were thinking about his son - well, it'd be nasty. To say the least.
You felt the same way about Lucius too. But that was a long time ago. Things change. Loyalties shift, and you realise that evil is evil no matter how attractively it's packaged. You would have given your life for him, back then, but you know it wouldn't have returned the favour. He never cared about anyone but himself. You see that trait in Draco, too, the selfishness, and yet you still haven't learnt your lesson.
Because there's still hope. There's hope that Draco's young enough not to have been completely corrupted. That despite the bravado, he's a good kid, beneath it all.
Kid. That's the problem, isn't it? He's a child. He's too young to fantasise about in this way. He's young, and he's relatively innocent, and maybe that's part of the appeal. You want to teach him, more than just Potions. About life, about love, about sex. About good and evil, about making decisions, about regrets and hopes.
You watch him, his pale head bent over his book or his cauldron, occasionally being raised to grin at you, or to insult someone else in the class. It's no secret that he's your favourite student, but it's hardly undeserved. You notice how hard Draco works in your class. You know that he doesn't devote as much time to any other subject. The other teachers bemoan the fact that he never works to his full potential. But for you, he does.
You know that it means nothing, or, at least, not what you wish it meant. Draco looks up to you. Draco knows that you and he are two of a kind, and wants to stay in your good books. There's nothing romantic or sexual about it. You wish there was, of course. But no. He probably sees you as an old man, someone who left youth behind a long time ago.
You think about Lucius again. You know that's wrong, too. Lucius is married, a family man. Lucius never cared about you. All you had to do was hint at the possibility and he would taunt and tease, taunt and tease, until you punched him. That, perhaps, is the only reason he still respects you.
You can easily imagine that Draco's response would be similar. Disgust, and revulsion, and finally mocking. History repeats, after all. And yet maybe there's still a chance. There's still hope. Maybe he doesn't take after his father.
But you see Lucius in his face, in his mannerisms. In the way he sneers at the other students, the way Lucius sneered at you. You know it wouldn't work, even if you weren't much too old, even if he weren't much too young, even if you weren't a professor and supposedly above that sort of thing.
Don't think about him. Don't.