Percy stands to embrace Mal, even though the movement is stiff and the emotion is hardly one of joy but he pushes through it because he doesn't want Miles to know that there's anything wrong, and he doesn't want Mal to feel awkward, he doesn't want her to know that he's here, full of anger and sadness that she's marrying another man and carrying his child.
He kisses her cheek. "Arthur is here as well, obviously. He's seeing Mr. Eames." Mr? He's turning into Arthur. "Maybe I should go and make sure they're okay-" he remains standing and offers his seat to Mal.
Miles watches the whole thing, but Percy doesn't think he picks up on anything being wrong. But then Miles always knows more than he lets on. Except he doesn't think the older man would let him get away with this kind of mess, and he hasn't made a move to stop Percy leaving, distracted as he is by his radiant daughter.
"I'll see you both for dinner, later," Percy says, and heads back inside with no intention of going to find Arthur. Because maybe one of them really could be happy.