Have you considered LibGDX? It's a Java framework that supports HTML5, Java for desktop (Windows/OS X/Linux), Android, iOS, and even Blackberry. It's also really easy to learn, and comes with a built-in scene graph package (which is very very handy for UI). If you want, I even have a class that can load in an XML format similar to HTML that's extremely nice for UI along with several example XML files, and I'd be perfectly happy to give you a copy (I've already given out a few copies to friends, and I've placed it in the public domain even if I technically haven't released the source yet).

If that's not up your alley, Cocos2d is a decent C++/HTML5 game engine.

You might be able to do it in RenPy also based on some other things I've seen it used for, though I'm not sure I'd recommend it for this (and I'd actually recommend not doing so as save games will become a pain once the game is bigger if I understand RenPy's save format correctly).

Obviously the final decision is up to you, just thought I'd give some suggestions, feel free to ignore me.

Also, and this is a bit of a stretch, if you need someone willing to help out on the project for free I'm always willing to do so. I have quite a bit of programming experience, and a decent albeit somewhat smaller level of experience with game development. I'm well aware this is likely to be a no, and that's fine, just thought I'd make the offer. I really enjoy this game and would love to be able to help out.