He blushes a bit more, eyes flitting from Rose to Jack. Apparently he hadn't thought of that question. "I...uh..."
His eyes flit back to Ianto, and he gets a concerned look, reaching for his hand. "Are you okay? It's okay, or...it will be...she pushes my buttons. It's only fair, I've pushed a lot of hers. And I do mean a lot. So many times..."
He looks from Ianto's face back to Jack's kissy lips to Rose, and rolls his eyes. "Oh, will you just stop it! Rose, yes, you can kiss whoever you'd...I mean, as long as you tell me and I'd certainly hope you're going to keep the circle small..."