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In
The Broca Divide when they were turned into primitive creatures, Sam and Jack had an altercation, where they seemed to try and mate each other.
In
Cold Lazarus a crystal being takes the place of Jack, and we learn more about how he and his wife dealt with the death of their son, Charlie.
In
Solitudes, Jack and Sam are trapped in Antarctica together, facing their end. I think that Sam kinda started giving into her feelings, as she comforted him.
In
There but for the grace of God while Daniel travels to a parellel universe, we find that Paralell Sam and Paralell Jack are engaged to be married.
In
Point of View, Alternate Carter comes to our reality, and is shocked to see that her 'husband' is alive once again.
In
Divide and Conquer, Sam tells Freya to retest Colonel O'Neill. When he arrives to the part of the story where he had refused to leave Carter behind, he is forced to make a startling confession: "I care about her ... more than I'm suppose to."
Carter is retested, too, presumably confessing her romantic feelings for Jack. The two agree that this confession does not have to leave the room. Only Freya, Teal'c and Dr. Frasier know about it for now.
In
Window of Opportunity, while Jack is experiencing the loops, he takes advantage of one of the loops. Resigning his commission, grabbing Carter, and kissing her passionately. Carter seemed to enjoy it.
In
Paradise Lose, while it seems that Jack may be lost on some distant planet with Colonel Maybourne, Sam confesses to Teal'c that after just losing Daniel, that she doesn't know if she can go on if they lose O'Neill.
Got a couple of these references from Gateworld.net. I've probably missed some. But those should help.
Rommie