It's good that there's no room in his heart right now for any jealousy. There's too much tiredness and warmth and worry and gratitude, nothing that can be squeezed out and replaced with any prickly, selfish feelings.

That, of course, doesn't mean the third party involved is going to be able to swallow the request so easily. What Kyoko will see when she looks Shinji's way is him looking awfully calm with the idea of all three of them whisk themselves away to one single bed. He gives her an even level look, sizing up the intensity of that kick of panic before actually answering Kai -

"Only if Kyoko wants to."

But, like, is she going to really going to tell him 'no' after that promise to spoil him? But he's not going to assume, or force her. It's up to you, Kyoko.