Of course he went to eavesdrop on their entire conversation when they go to Jingyuan's room. He remains there until they start with the unholy parts, rolling his eyes and leaving. He sure finds their dynamics weird, but also can't know their whole story, let alone their individual ones.

He returns to the kitchen to mind his own business and after some time, Leaf comes there to cook.
He observes the other who prepares the most decent meal he can with what they have left in there, but then doesn't eat.
After cooking, Leaf just goes to the couch and falls asleep relatively fast. He didn't eat in two days, but others can assume he ate something during his time out of home. It's just that he doesn't feel hungry after doing 'that'.