I'm so sorry
I'll try to give as much information as I can. The last time I heard this one was like two years, about a year and a half ago or so. I heard it a good handful of times, back when I worked at Old Navy. This particular song came on periodically throughout August 2013-February 2014. I've been looking for it, pretty much since the very first time I ever heard it, but no luck. Lately, it's just really been on my mind, like I really need this song in my life.
From what I remember, it was a synth-pop indie type song, very sentimental sounding, almost kind of on the sad side. Vocals had an echo effect to them. It was a duet between a man and woman. The male voice kind of sounded almost like Bombay Bicycle Club, and the female voice was a cross between Chvrches and Haim. It had a slower beat to it. I remember that it started out with the male voice, who sang something I can't remember, and then the chorus would be sang by the female voice, which sounded something like "yooooooouuuuuu (she stretched the "you") could never be..." something, something. And then the synth-type instrumental would kind of echo her vocals. Then it would switch back to the man voice, who says something like "the quiet moment, is getting stronger", or "the quiet moment, is getting longer", something about moments and getting longer/stronger.
I'm so sorry if this is vague, but I've been going crazy trying to find this song! Any help is appreciated! :)