One of the crappy parts about dealing with a person who lies is that they often lie to themselves; they set up a little fiction of sorts in their heads and stick to it. Because they can't be honest with themselves, being in a relationship with such a person can be stressful at best, but at worst...I can only imagine.
Obviously, he needs some sort of help, but if he's not willing to take that help and use that help, splitting up is probably the best.
I've never been a big fan of marriage, mainly because of the whole divorce thing. But this situation truly seems like an obstacle that was insurmountable, and you have to ultimately do what's right for you, and what's healthiest for you. It's painful, no doubt, but it seems like you are strong enough and clear-headed enough about it that you'll come through it okay.
If you find yourself with a need to talk about it, I hope you'll avail yourself of the opportunity to talk to your friends here and at KFM (as you know, this is a strong community) and those friends closest to you. When my folks died (obviously a totally different loss), I found the greatest solace in my friends; just being able to talk.
I know different people deal in different ways with problems, but should you wish to talk about it, I'm pretty much available for listening. Lemme know if you wanna AIM, and I'll give you my screen name.
Man. We could seriously have a discussion about all the frighteningly similar parallels between our two respective not-so-good relationships and have about a month's worth of subject matter.
just a big virtual hug from me to you
it will be ok in the end sweetie