Draco has always known of his homosexuality and has never hidden it. The only thing he hides is his obsession with Harry.
Harry doesn't care for Draco, really, but he'd like to tap that ass.
They do the nasty and somewhere along the lines they fall in love
Ron is straight, but his longtime love for Harry overrides his sexuality.
Harry is gay, but doesn't start to like Ron until Ron starts to get hair and muscles. His feelings for Ron are more sexual than emotional.
They fall in love, but probably don't stay together for more than a few years.
Ron still has the hots for Hermione, and if Harry is in a good mood he'll let Ron invite her over for a fuck with the two of them. Harry, however, never touches Hermione, because vaginas make him queasy.
Snape falls in love with people all the time because he is so lonely, but he rarely acts on his feelings. He is sexually flexible and secretly latches onto anyone who shows interest in him. He never has long-term relationships because he has trust issues. Sorry, Snapers. :(