Your connection to Jack is that he hired you then immediately betrayed you for (in the words of Torgue, the not-so-secret-conscious of the writer) "REASONS!" They try really hard to make you hate Jack from the outset, it doesn't evolve as a consequence of what he does. Your hatred of Jack is based on the voice skills of a guy playing a smug jackass who you don't get to kill until the end of the game. I suppose there were a couple times in the story where he pops in and shit happens, ambushes and what not, which kind of actual made him more than some guy who won't shut up. But I sensed early on how desperately they needed you to hate this guy for the story to be worth a shit, and I wasn't getting on that train, because I unlike the protagonists, am not a complete fucking moron.
And that's always been a gripe of mine with BL, since the first. You as the protagonists are silent morons doing as you're told and being duped by people (the writers) who think they're very clever with their twists and funny with their taking the piss out of the whole story at the end. You're a meat puppet in someone's absurd story. It's why I can't ever get attached to anything in BL. And why I don't buy it until it's stupidly cheap or someone bends my arm. It's a decent game on all fronts, but unlike a lot of decent games, it makes me regularly slap the people that make it. To which I'm sure they'd reply "Huhuhuh it's Borderlands, that's one of our design goals!"
Actually, I take something back. I am attached to something in BL. Torgue. He's the only honest fucking character in the whole series. He's the only character that actually lives the theme without muddying it up with serious vs. FUCK YOU plot threads. He just screams and is absurd and loves to watch shit get blown up. I can appreciate the humor without feeling like some of it is at my expense.