Alright, because you asked....
I must say before I answer your questions that H/D as a category generally has me rolling on the floor laughing. It's just so hilarious- I love slash, but H/D seems incredibally unrealistic to me. But, some of the most touching slashes I've found have also been H/D. It's a delicate pairing to work with.
Now, with that said, let me commence.
Draco is confused by Harry's actions, and wants to talk to him without being straightforward about questioning Harry's sexuality. How would he do this?
Well, I'd say it really depends on how old they are. I'm going to go on a hunch and have them as fifth or sixth years. I'm also going to assume Draco is gay as well.
So, you could have them both wandering the corridor late at night. Draco would make some rude, nosy comment and soon they're arguing until one of them slips. Or, you could have a sort of reverse-Sectumsempra (the chapter, not the spell) effect, where Draco finds Harry in one of his reflective moods under the tree by the lake or something and asks him what he's thinking about and it leads from there.
What seems most logical, though, is just Draco making a snarky insult and then Harry blushing at the wrong moment and revealing his secret. Like...
Draco wheeled around in the empty hallway, cocking his eyebrow. "What'd you say?"
Harry's eyes narrowed. He cleared his throat. "I said," he said, taking a step towards Draco, "that maybe you would look less like a ferret if you took that smirk off your face sometimes!" He stared intently at the Slytherin boy, who took a step back, laughing but still mad.
"Bloody hell, Potter, what are you, queer or something?" Draco shot. Harry stumbled back, blushing and hanging his head.
Draco paled. "Bloody hell. You are, aren't you?" Harry's head gave the barest of nods.
Aw, now you've got me wanting to write an H/D!
Draco's attitude towards Harry is changing dramaticly, and Harry doesn't know how to accept this. How does Harry react?
Harry's kinda thick, so he might not notice right away, but when he did I think he might wait and observe for a while. Then, he would confront Draco about it in a very straightforward manner ("Yes or no, Draco!"). He might be rather shocked to find out the truth and try to ignore it at first, but then would come to accept it. Hopefully.
After quite a few confrontations, neither Harry nor Draco are willing to open up to one another. How will they gain each other's trust after 4 years of complete loathing?
Nothing brings people together like a few hours spent together late at night, I always say. ;)
Detention works, too. And near-death experiances. Or maybe just a simple talk.
Hope this helps!