This is weird. Its normal to have a crush outside of your relationship. It's not healthy to act on it or to emotionally invest in this crush. You made a commitment to be with each other and she's emotionally violating that whilst assuaging her guilt with radical honesty with you.

This is no good in my eyes and reeks of disrespect.

You wanna fuck this guy? Fine go ahead we're done, you just threw away the last 2 years for a casual fling, hope you enjoy it and will be able to handle me completely ignoring your attempts to restart us when it comes crashing down.