I know him so well
There's something deliciously hot when a guy is singing a woman's song (the contrary is true too... One of my favourite part of Across the universe was the slow version of "I wanna hold your hand" sung by Prudence)
So the original context is the wife, Svetlana, and "the other woman", Florence who both come to term with the ending of their respective relationship with Anatoly (who is equally screwed by the plot later on).
So despite regrets and bitterness, and the fact they both loves him so much, you can see the girl moving on while trying to cling on the good memory.
The part that hurt is that they are are clearly still enamoured with him and trying to justify the failure as their own fault. Svetlana thinks she wasn't adventurous enough while Florence thinks she couldn't provide him the security of stability.
John is singing Florence's part.
You can listen to the entire part of Faenol Festival where John sang but there's only one day left.