Yes, Kirk is probably the top probability if he were to hook up with anyone else, though there are others like Wade and Martha, the other people he turned to for variety during those long years in the fictional future. Even if it was fictional, the AIs had probably got the right bunch of people.
Ianto's admission that he did listen even if he appeared not to be is a huge relief as well, and means a hell of a lot. He sets his paintbrush down carefully and then comes down the ladder so he can sit on one of the lower rungs, giving Ianto his full attention.
"It's not even about not wanting to be with you forever," he says, because this is the one part of it that they still don't seem to be communicating properly. It's the part he felt Ianto didn't understand in their argument in that future, and it still seems like they're on different pages.
"I do want to be with you. Okay, possibly not forever, because I daren't even look that far ahead, but when I do look ahead, I can't imagine not being with you. I don't want to not be with you. So it's not about not wanting to be with the same person, it's about not wanting to be with just that person. Not wanting to limit the possibilities. Not wanting to commit to forever, with just you."
He laughs, rather uneasily. "Which is an odd thing to say when there's Spike as well, but I think we all know I don't feel the same way about him as I do about you. But... god, does this make any sense? I just... I'm not about to go off shagging anyone and everyone, because I know it's important to you that I don't and honestly, apart from perhaps Kirk, there's not a massive amount of longing anywhere anyway. It's just that if something does happen, if I feel that connection and want to take it further, or I have a scratch I need to itch that neither of you can take care of, I want to be able to do that - hopefully being able to give you advance notice - without losing you altogether."