Hilary Duff and Mike Comrie -- We're Not Saying They're Banging, Buuuut ....

Hilary Duff and her ex Mike Comrie have been separated for almost a year ... which begs the question, why the hell are they still going to parties together and holding hands?!

The "Lizzie McGuire" star and former NHL player hit up the annual Casamigos Halloween bash in Los Angeles Friday night and proudly held hands in front of the paparazzi as they walked inside.

Back in July it seemed they might reconcile ... which means it's possible the couple is back to banging -- or maybe they're just the coolest exes ever.