Wow. Tough cross to carry Gord.
I am no professional but I am a firm believer in marriage. If i were you i'd seek professional help, not for her, but for you.
After reading your post I tried to put myself in your shoes and it's so hard because it's such a huge burden.

But as best as i understand it, if I were you, I wouldn't leave, if just for the kids' sake.
That said, (in order to help me cope), in my mind I would try to emotionally detach myself from her a bit and not to try to make her burden, my burden.
Make it so you almost view her as a house guest. You know, toodle about your business...let her do her thing...you do yours. I guess it'd be almost like treating her like you enjoy having her around but you don't HAVE to have her around. Be cordial, be nice. Involve her in dinner decisions etc...
Yeah, like a house guest is the best way to put it.

So yeah, if I were you, I'd try go about my daily routines. Perhaps go out with friends in the evening.
Show her I'm having a good time and that I can carry on without her. (even if it is fake).
Take the kids places. Get some exercise. Have conversations with her about her internet use that aren't threatening....like I might have with a guy friend who's into that kind of internet stuff. I'd almost be tempted start my own Facebook internet page and start an online freindship with her as an alias.

I'm not meaning to make your situation sound light. Please don't take it that way. I know a bit about what it is like to have a wall between you and your wife...and it's ain't fun. An my wall isn't half as tall as yours.

all the best