Sebastian never saw the musical.
He sometimes wishes he had, but those moments are rare. They come in odd intervals, surprising him when he least expects it, and he wonders if having seen it would help him stop what he knows is coming. As it is, all he has is his imagination.
When he imagines his part in this sordid tale he sees himself as an unfortunate spectator to it all, a lone figure caught in the audience, he can only stand and watch.
The stage is set. The final act is coming and he is powerless to stop its climax. He wants to scream, to shout, to curse them all for their stupidity, tell them to run, run, and never look back.
He wants to reach out a hand to the Phantom and say, "I will love you. I will stay. Give me the chance. Let me stay."
But instead he places a hand on solid wooden door in front of him and listens to the sound of Jim rutting wildly against John Watson.
This, he thinks, is surely the lowest level of hell.