The game does slow down for me here when I leave it running for a while. (MacBook Pro, Chrome)
I don't know if it'll help, but there are some parts of your code that are constantly running and may not need to.
You could put some of these things into event groups, and enable/disable them only when the checks make sense, like the dialog code. Other things, like the fallspeed, might only be necessary when the platform condition "Is Falling" is true.
It could be something more technical; maybe there's something in the debugger that can provide clues?