Jack hates having to do this to anyone.
He'll never forget the day he woke up and realised he couldn't remember the day before, or the week or two whole years before that. The violation infuriated and sickened him. He didn't understand how or why the Agency could have done such a thing and now he does it on a regular basis.
At least the Retcon pill he's perfected is an improvement over the techniques the organisation was using when he was "recruited." Those who actually survived ended up populating the madhouses of nineteenth century Cardiff. It's not much of a defence, but it's the best he's got.
Usually, he can rationalise that people are better off forgetting what they've seen, but what the hell has Gwen Cooper done to deserve this? She's displayed the same tenacity that attracted him to Owen, the same ingenuity as Toshiko, everything that Torchwood usually rewards.
The sparkling green eyes and long black hair combine with her unrestrained laughter to make him wish there was more time to enjoy her company. Suzie and Owen have had a falling out and that's put an end to his most recent arrangement. Jack is never lonely for long. He knows the dangers of his own habits, but isn't prepared to give them up either. Gwen's smile as he tells her about Torchwood and watches her bristle at his callousnesss reminds him that there's always a room nearby. Yes, she has a boyfriend, but lots of people have boyfriends or girlfriends. It rarely stops them or him.
It would be so easy and yet so hard. The only thing worse than taking away memories is taking away those memories. He won't do that. It's not fair to either one of them. None of this is fair. Torchwood. The Doctor. Weevils. The whole twenty-first century and the job he knows he has to do here. A job that could be ever so much easier with Gwen Cooper around, but won't be because those are the rules. The pill is in her drink and tomorrow she won't know his name.
It really is a tragedy.