"I won't." It's such a surprise and a relief to have it go this way. Maybe it shows how much they've both changed in the months they've been here. He feels abruptly embarrassed for not trusting Jack with this to begin with. Maybe it would have helped.
"I'm worried about him," Maybe he should make an effort to stay calm, to hide the obvious fear and unhappiness he feels since is about the other man he's sleeping with. Even if Jack is better with jealousy than most people it might still be hard to see how much he cares.