We do not know how committed Lance really was to making things right between him and Kristin. It's not possible to be a full-time wife to a half-time husband, and even if Lance did physically stop taking his business and heart outside the marriage, he may not have been committed to a full-time marriage. This doesn't sound like that last object was his goal, when his current conclusion is, "We're truly committed to maintaining a good relationship, but not a marriage."
I've heard from people who've suffered the devastation of adultery and then tried to rebuild their marriage. Once that trust is broken, it takes an enormous amount of work (and length of time) for the couple to baby-step their way back to a decent, loving, healthy relationship. The root reasons why the person broke marriage vows has to be found and corrected. A marriage can't be rebuilt by just showing up for dinner and sleeping in the same bed.