Whilst I wholeheartedly agree with all you say, at the end of the day whatever people's reasons for the decisions they make may be, pairs skaters don't have to keep skating with someone else if they no longer want to skate with that person. That's true regardless of what kind of human being they are or what their reason is, so I am not really sure a conversation about this can be productive if that makes sense. There is a lot I would actually like to say about Coughlin but none of it would fly on this forum

and unfortunately it wouldn't change the basic fact that he did have the 'right' to change partners.
In general I think the frequent splits of (relatively successful) North American pairs are a pity and rarely work out well (for exhibit B one need only look to Kirsten Moore Towers, a far more likable character

) but at the end of the day these people are people not just skaters and have to make their own choices about who they want to skate with and why.
I do wish we had been able to see more of Caitlin, she was a truly lovely skater.
LOL -- I actually said initially that it's not a conversation to get into here, but yeah, as it happens, I am responding to subsequent comments addressed to me.
People change partners all the time for different reasons. In this instance, I do not think it didn't work out for Denney/Coughlin. They were actually good together, especially technically. But aesthetically and in terms of finding the right overall packaging for their strengths and personalities, I don't think they quite achieved that. But they were very competitive internationally, as they built their fairly short-lived career. Injuries hampered their progress in the end.
What I wonder, is whether or not the Caitlin/Coughlin split was great overall for the trajectory of U.S. pairs at the time. I know that's not realistically a consideration, since U.S. fed can't force partners to stay together, if they want to make a change. Still, couldn't there have been more conversation to find out about why they were splitting, in light of the fact they had just broken through at Worlds, which was a promising development for U.S. pairs? I don't know if any conversations were had with all the principals involved, but I doubt it. Probably U.S. fed and Sappenfield didn't persuade Coughlin against the split, since Caydee Denney was highly regarded, especially for her jumping ability and her lively personality. Yet, it's not easy (as we know) to simply partner with someone else and expect immediate results, similar results, or better results.
At the very least, why didn't U.S. fed take a larger role in trying to assist Caitlin? As it turned out, Caitlin partnered with Josh Reagan, but seemingly they were more romantically attracted than anything else, and their skating partnership never got off the ground. The promise that we saw and loved in Caitlin was wasted. By the time, she paired with Hamish Gaman in the U.K. (they looked quite good together aesthetically), she had lost some technical abilities, and needed monetary resources and good coaches to help get back to a high competitive level. It was not to be, which is sad.
But, nothing is promised or guaranteed in life or sport.