I always thought of Sam and Mikaela's relationship like many that we've seen in high school. Not a whole lot of those manage to last. As time goes on, you start to drift off into different areas and goals in life. I can't help but wonder if Sam's rather upscale lifestyle did clash with Mikaela's. I could imagine that becoming a heated topic of arguments between them regarding the difference between their family lifestyles. In the end, Sam needed someone a bit more down-to-Earth. Someone with a little less baggage. And from seeing him with Carly, she doesn't seem to have as much as Mikaela does. The only major baggage is that her Brother was killed in wartime action, but she doesn't seem to be one become too overbearing in a relationship. Though I'd believe her as a British Embassy official moreso than Denise Richards as a Nucular Physicist.