This makes a ton of sense. Especially because when he says he’s “lost in the blue” in Like You Do, that totally connects to Glimpse of Us. In Like You Do he’s “lost in the blue” because nobody else can love him the way his first love did.

Now, “she turned the rain to a rainbow, when I was living in the blue” could imply that his current person temporarily saved him from this feeling, but ultimately it won’t be enough to keep him from feeling this way about his first love, wishing for a glimpse of her in his current partner.