It was difficult for Ianto not to be jealous of Martha. The moment she waltzed through the door, Jack got a bright smile on his face. He hugged her; he confided in her. They'd been through the end of the world together. It was like pulling teeth to get Jack to talk about it any other day, but with Martha here, he kept bringing it up casually, and Ianto could tell that Jack's swagger and bravado were more than show. With Martha, somehow his experiences didn't hurt him as much.
Ianto wished Jack had taken him along on the journey. Seeing the end of the world didn't sound fun, but meeting this Doctor had to be amazing. People at Torchwood 1 and Unit had talked about the Doctor all the time, some with delight, others with contempt. Jack thought the world of him. He'd come back from his whirlwind adventure with the Doctor more flirtatious than ever. There was an obvious pain he felt from seeing the end of the world, dying so often, and realizing his Doctor couldn't fix him, but Jack didn't like to talk about it. He wasn't as dark as before; he'd accepted this as his lot in life and moved on.
Only Jack hadn't moved on. Ianto could see it, in the moments Jack stole with Martha. Jack was overly concerned for her well-being, and he kept reaching out to see if she was in as much pain as he was. Their connection was unbreakable. Ianto shouldn't have been jealous, but he was.
Then Martha mentioned the little, red cap.
Ianto shivered. He wasn't "out" to the world, but he wasn't exactly hiding either. Everyone in Torchwood knew he was bi... except he wasn't really. It wasn't men that Ianto was attracted to. It was one man: Jack. There was no point being embarrassed by it. Especially when he saw the curiosity and intrigue in Martha's eyes. Was Martha jealous of him?
"Well, red is my colour," Ianto said. He shivered again, this time thinking about the role play he'd do with Jack while wearing a little, red cap. It was getting difficult to concentrate, and Martha was pressing him for details.
His jealousy melted, and his confidence returned. When Jack had said "I came back for you," Ianto couldn't tell if it was a line or not, but things had changed since Jack returned. Jack wanted to go on dates now, which was odd, but amazing. He didn't wait for the others to leave at night before initiating a quickie in the office. Their entire relationship was barreling forward, but Ianto didn't want to oversell it to Martha. He focused on the sex. He was confident in the quality of their sex life, and he didn't mind boasting. Jack was envied by all (and flirted with all), but he was faithful, and he was getting better at letting Ianto know that what they had together was important. Making an excuse to leave Martha, Ianto trotted upstairs, grabbed his stopwatch from his desk, and went to find Jack.