Much was caught off guard by how happy Marian was to see them - in his head she already psychically knew what they'd done, so he was a bit stiff with surprise when she first pulled him in. Or maybe guilt. No... it was definitely surprise. He did not feel guilty.
Seeing Will happy after spending the night with a very unhappy Will was good though, and after that first awkward moment he hugged them both back as hard as he could. He was uncharacteristically quiet though, but maybe that was just him being considerate and letting Marian speak first, before he had to...