To be honest, Jack hadn't planned to return to Torchwood.
When he ran to the TARDIS he wasn't thinking about Cardiff and the life he'd had there at all. As far as he was concerned it had been a good run and it had been fun, but that chapter had closed. He thought he'd move on like he always had. But soon his heart, the unpredictable, passionate and infamous heart of Captain Jack Harkness, started to miss Torchwood.
The excitement, the chases, the people. Especially the people. He missed Gwen's tough-as-nails yet vulnerable attitude, along with her big eyes and the lovely tint of normal she gave to his bizarre life. Tosh, so smart, so pretty, so lonely. He felt like he'd abandoned her when she needed him most. He'd promised to take care of her, and the taste of an unkept promise was bitter in his mouth. Owen, so abrasive and yet, endearing. Like a kid that needed a father. Jack genuinely liked the difficult doctor, and missed the faux carefreeness Owen had about him. And then there was Ianto. Jack's heart ache with the void Ianto had left. He had, for the first time in his very long lifetime, fallen in love. Ianto was honestly kind and caring, and loving and giving. Always there for Jack, knowing exactly what he needed, when he needed it, and giving unconditionally. He hadn't set any limits for Jack, giving him things his other lovers hadn't, things like coffee when he needed it most, or backrubs, or a cheer-up kiss. Or simply been there, simply cared. It was a real relationship, not the string of fucks Jack had to his name, or the quasi lengthy relationship he'd had with John in the time loop. Not to mention, young as he was, Ianto was one of, or the, best lover Jack had ever had. It had been ages since Jack had gone three times in one night, and it was also the first time it had been with the same person all three times.
Jack loved him, loved them all. So he smiled at the doctor apologetically and asked to be taken home.
With a grin, he stormed into the small house and blew the fish-man's brains all over the wall. He was home.