they did? in fact they cleary slept together for the entire 'camping' time in the 7th book. they had probably slept together before this, before the end of the 6th book in fact.
see, chapter 15:
'early next morning, before the other two were awake, harry left the tent'
therefore hermione and ron are clearly sleping TOGETHER as a couple.
then the part where ron has come back (at the end of chapter19) and it is night time we are told what harry sees and hears:
'hermiones muffled voice from beneath her blankets, but harry saw ron smiling slightly as he pulled his marron pyjamas out of his rucksack'
there were a couple of other examples too, but this entire thing shows that they are clealry a couple who sleeps together.
see, chapter 15:
'early next morning, before the other two were awake, harry left the tent'
therefore hermione and ron are clearly sleping TOGETHER as a couple.
then the part where ron has come back (at the end of chapter19) and it is night time we are told what harry sees and hears:
'hermiones muffled voice from beneath her blankets, but harry saw ron smiling slightly as he pulled his marron pyjamas out of his rucksack'
there were a couple of other examples too, but this entire thing shows that they are clealry a couple who sleeps together.