The thing is QS, she is negative about staying married to you... She's just putting a positive spin on it...
And the "happy" you are seeing is the high she's getting from the fantasy she has in her head : the divorce, the OM, etc... It's NOT a healhty happiness.. it's an artificial high much like gamblers' get when they are on a winning streak.. they DO crash and they DO make a mess of their life, but when they are "on a roll" they do appear to people as genuinely happy...