Poor Cupid Reaper is just trying so hard and Sunshine is too selfish and too caught up in this idea that he can somehow just make things happen and that everything or anything that goes wrong is because someone else lead him there, someone else mad the bad choice.
He is literally being told this is your miracle, this is your best chance, it won't get better from here but because it takes recognizing his own faults... Sunshine can't do it. He can't start from nothing because that means admitting that he fucked up so badly in the original relationship that he can't come back, admitting that he made the mistakes and now has to make it right all on his own.
I think the hardest part is knowing that Sunshine could make this choice, he absolutely could, and yet he can't because making this choice right now just isn't something he's capable of, not now.
He is turning away from the light. Oh my fucking sgjkldgdf he is literally, and metaphorically, turning away from the light because the light that Q offers is illuminating a world he cannot bear to see.