I think it's about a partner who has ambitions for their life, and they've put relationship priorities aside for them. They lied to the narrator about wanting him more than anything.
He'd rather end it now then being in a torturing relationship where he cares way more than the other person. And now, he doesn't can't get himself to his partner like he used to, because of all that wasn't true. He can't see the rainbow anymore, so even if things did change, he wouldn't be able to put it behind him.
I think it's about a partner who has ambitions for their life, and they've put relationship priorities aside for them. They lied to the narrator about wanting him more than anything.
He'd rather end it now then being in a torturing relationship where he cares way more than the other person. And now, he doesn't can't get himself to his partner like he used to, because of all that wasn't true. He can't see the rainbow anymore, so even if things did change, he wouldn't be able to put it behind him.