The mention of sin here and the devil made me think there is no redemption for this relationship. The line about the moon made me picture you both studying the phases, finding the wonder in constellations, and bonding over the night skies. But this night, there is stillness, a silence. Nothing special in anything, really. And no one is willing to address each other honestly. Confessing to the devil immediately gave me the indication that one person cannot admit the indiscretion. The other person knows, and perhaps doesn't need confirmation (possibly infidelity?), but it's the fact that they can't even say it aloud or take responsibility for it that really sets the tone for how they could ever proceed forward.
I cannot get the image of wanting to place the sun between two people for warmth; it's such a sad request in a way, and like a last plea, something that feels impossible but will bring you both some final remaining light.
I also felt such immense sadness at these lines, and loved how you use "avalanche" as a verb:
"a chunk of memories break
off and avalanches onto
The next question, and confirmation almost that you cannot forget, felt so profound. Like you are both burdened by the weight of what you became, and it's too heavy. Even if there were blissful times in between, sometimes the journey and the burden of remembering is too much for a fresh start. Or for a second chance as implied earlier.
The time passing, despite your best efforts, the light dimming, is really a sign of that farewell. I also took "aligning the stars" as this being fate. As painful as it is, there is no way back to that spark, to that open space between you.