Ianto normally wasn't a very physical affectionate person, but with Jack things were different. He would allow Jack to do things that no one else had been permitted to do with him, even Lisa. The way Ianto felt about Jack had changed everything for him, and Ianto was completely fine with it. This also meant that Ianto liked to think that he understood Ianto in ways that most other people didn't. So, he recognized the sigh and knew that Jack wanted the embrace to continue.
But since he did want to find out what was going on, he listened to what Jack said about where they were. But it also didn't take long before Jack was pulling him in and kissing him with enough passion to bowl the man over. Of course, Ianto welcomed, and he even allowed his body to press completely against Jack's.
Ianto noticed the longing in the other man's words and Ianto knew that Jack had been dealing with his something here that wasn't normal. But Ianto made a promise to himself that he wouldn't ever leave Jack again if he could help it. "I am all yours" he promised, knowing that he had every intention of keeping that promise.