Back buttons would probably not be too hard to code in unless some variables were changed in which case you suddenly have a huge problem. You’d have to restore any variables that changed as a result of the last choice.
As far as I can see there are only two ways to do that effectively. Either saving a copy of all variables before every choice (and keeping them so people can go back as far as they want) or having a ‘back’ option coded at every choice so you can undo whatever changed at that point.
I suppose you could pack variables into strings. That would, at least, reduce the number of duplicated variables you’d need to create but it’s messy. I was thinking about doing this as a sort of restore point at the start of each chapter. A proper ‘save’ option would be better though.