Number one, at the bar, is all passion and aggression. There's violence in the kiss, and there's love in the fight. Two equals battling each other for dominance, a dance they know inside out, the knowledge that at the end of the day, they can trust each other with their lives. *

Number two, at the rift, is John's last chance. His last chance to convince Jack to come with him, or to let him stay. Jack is all passive, but then he keeps his eyes closed for a moment after the kiss is over and you can tell there's something there.

Number three, at the hub, is nothing but a sweet little peck on the cheek. John is taking it down, reining himself in, accepting that he won't be able to drag Jack away. It's goodbye, and it's surrender. John has lost a battle, and he's leaving the battle field with as much dignity as he can muster. He just hopes Jack didn't see his hand shaking.

*No, I haven't forgotten that John killed Jack. Twice. And buried him alive. I've just come to the conclusion that when he pushed Jack off that building - he really didn't want that. He was just throwing a tantrum because he didn't get what he wanted and given his physical strength a tantrum is a very bad thing. When it was done he instantly regretted it. And hey, you don't get sent to murder rehab for nothing...he does have an impulse control problem obviously. And the second time doesn't count. Neither does the burying alive.