Before she leaves you can make yourself scarce, so she can have the entire space of your property. While you make yourself scarce, your having fun and doing what you want to do.
Pieces of all these sitches sound like mine. What you said "TO her she HAS TO LEAVE, because she feels it is the way to happiness...getting rid of me is happiness for her.", I don't know how they got to this point.
I worked on it and I believe as a result of the affair, we become an impedent and threat to their affair - which they correlate to happiness.
Its how we become an enemy and we didn't do anything.