This is what I thought Sweeney was thinking in the final scene of the movie. Enjoy!
There was nothing he hated more than lying.
And that's exactly what she'd done. She'd lied to him in the worst way possible, for her own selfish needs.
Something inside of him snapped then, and he decided on the perfect way to end her days.
She had lied to him, and so he would lie to her. It was that simple, like an easy algebra problem.
Dancing with her around the room, he pretended that everything was okay, that he'd put the past behind him. But everyone knows that he never let anything go until the ones who'd done him wrong were taken care of.
He saw the opportune moment when they passed in front of the furnace. Throwing her in, he felt satisfaction well deep inside of him as he heard her tortured screams of pain.
Then the sadness set in as her yelling came to an abrupt stop.
He made his way over to the only one he'd ever truly loved, cradling her body in his arms.
He began to sing, retelling the story of how this had all come to be in the first place.
He heard the sewer open, heard his forgotten razor being picked up off of the floor.
It was then that he decided that he deserved to die. He had nothing to live for.
Raising his head, he gave whoever was behind him easier access to his neck. He felt the razor pass over the skin of his neck quickly, felt it plunge through the comparatively thin layer of skin.
Yes, he deserved to die. He had lied time and time again to countless people.
And after all, there was nothing he hated more than lying.