With the aircraft swap, I lost my E- aisle seat which I was fine

However I was re-seated to E+ (good thing) but in a middle seat (bad thing)

I take it there is not moving within E+ once you are seated there without paying?

Is there ever a time that will be allowed without charge. The seat next to my GF (window seat) is open and she is in the middle two rows behind me. If that stays open will there be a time I can just move there or is the only way to fork over the $139. the flight is tomorrow a.m. early. about 12 hours from now.

thanks