Darkness, yes. Obviously, Gwen has a thing for Jack; obviously, Gwen is something of a slut. Either Jack has some altarboy morals hiding in his coat pocket, or he simply doesn't find her as appealing as he does the damaged and surprisingly deceptive office boy. (Because, honestly, as much as Jack preaches about Gwen's life-outside-Torchwood's being important, I don't think that alone would stop him from bedding her just the one time.)

As far as competence, Ianto is a little terrifying. Sure, he could have, you know, brought about the subjugation of his entire species, but he's got a good head on his shoulders. And, hey, he's definitely good under pressure. Realistically, though, I think Jack calmed down, took one look at the kind of asset Ianto really could be, and went about keeping him.

I make no claims as far as a perfect reconciliation with the ante (aka "let's set up some dramatic action, Ianto's disposable") and post ("hey, he's pretty likeable and has awesome timing, we'll keep him!") storylines. I dare say it would take TW retcon rather than traditional retroactively altering continuity to make canon make sense. I like to pretend that Ianto has bad nights and panic attacks (and possibly some hardcore anxiety medication) that we don't see. Because, let's face it, this is Torchwood, and all the good stuff happens off screen anyway.