Meaning of the title

It's a line from the film.

Paul: Would you turn that light on above the bed?
I don't want to be in the dark with you.

probably symbolizes several things, but here, Paul was finally getting his life back together, they finally met up, and Paul even says "You're not supposed to be naked" and "We're not having sex".

Recovery 101 says get your OWN life 100% back in order before you get involved with others (especially one who may ENABLE your old habits).

I think he was finally trying to follow the rules of recovery, and wanted to make sure he didn't mess it up by breaking the rules, and it would be harder to break the rules with the lights on.