Johnny, I've been thinking about this thread since this morning. I hate to tell you this, but while libido differences and her self-consciousness about weight gain may factor in a bit, she frankly is acting like a woman who's indirectly trying to tell you that she "wants a bit more space in the relationship," which generally translates to "wants out." Instead of dealing with you directly and telling you that straight out, she's not getting pleasure anymore from sex, not feeling like physical intimacy, flirting openly and hugging other guys in front of you, and getting angry. Sorry to put it this bluntly, but it really does sound to me like she's essentially saying she's not that into you anymore.

I know this wasn't the answer you wanted to hear, and I certainly didn't write this to be hurtful. I know this must be horribly painful for you. But I think you might need to consider this possibility. And if you want to spare yourself some future pain and can stand to, you might even ask her directly and see if she'll tell you honestly that that is indeed what's going on.