^^^Do you guys not remember that Callie worked at Mercy West before returning to Seattle Grace? Do you think she made no friends at all during her time there?
I did forget this but even so how long did she even work there for and what are the chances she became friends with Jackson. I mean there was no indication given prior that Callie was friends or even a casual acquaintance of Jackson's, not enough for me to understand why she would have invited him to her girlfriend's birthday party. Maybe it was just an open invitation to whoever though, all surgeons or something.

ITA. There are plenty of ways couples can have "issues" without cheating being involved. Sadly, i don't have a whole lot of faith that the writers will come up with something other than "Callie still likes guys remember so let's have her kiss/blow/screw one".
That's how I feel. I feel like it would be natural for them to have disagreements over stuff involving life choices, their future etc but it would be easier and more dramatic for them to have Callie cheat with a guy but it would be completely and totally out of character. Callie wouldn't tell someone she loves them and turn around and cheat on them, especially having had the experience of being cheated on by her husband. The way Jessica Capshaw said people do stupid things, kiss the wrong people etc just gave me a bad feeling b/c some people do, Callie doesn't. She's not Addison or George, I just don't feel like she has that in her character's make up so it would come out of left field for her to do something like that and hurt someone in that way.

If Izzie is pregnant its another totally ridiculous storyline for Izzie especially considering they made a whole drama out of getting Izzie's eggs frozen and mixed with Alex's sperm before she underwent chemotherapy. Also if she's pregnant and presumably is back to tell Alex he'll be so devastated if she has no intention of coming back and plans to raise the baby on her own. She can't do that to him, he's a hardened ass on the outside but we all know how much that would kill him for her to be pregnant and not want to be with him or let him be a father. Also I wonder if this is potentially leading up to Izzie dying and leaving Alex a single father, or even worse Izzie dying and losing the baby, or even worse (for the audience) Izzie NOT dying and losing the baby.