I've had many times after termination when I was doing fine until I realized it was because I wasn't missing T. That realization was the trigger to feel bad again. When I didn't miss him, I was admitting he wasn't present in my life anymore, and admitting that was painful. That's when I needed to feel connected again and started missing him again.

I hope that makes sense...

I agree with the others that it's two steps forward and one step back. Be gentle to yourself. You'll get over her at your own pace.