It really is more than he dared hope for. Something actually involving the three of them as a unit, rather than a tug of war with Ianto in the middle. He knows as well as Spike does that it will take time to work up to that, but to have it as something to aim for, to work towards - that's fantastic.
He lifts his hands slightly in surrender, smiling ruefully. "I know, I know, I get it." Well, not get it in the personal sense, but he's negotiated with enough people who're new to polyamory by now to at least be aware of how they usually handle it. "It's a lot. It's a lot for us to work through. I'm not expecting miracles right away. It's just... it's not just Ianto, is it? There is something between us too?"
And it's not easy for him to admit to this either. He may be free and easy with his body, but his emotions? Not so much.