The proper answer to "are your changes just to win me back" is to emphasize that you now realize you needed to make these changes, and will continue making them whether or not the marriage succeeds.
They (understandably) worry that the changes are just for show and that you'll revert to your old self as soon as they recommit to the marriage.
But they're also feeling uncomfortable with the fact that the things they used to justify their affair don't look so real anymore.
