Sounds like you need a new girlfriend as a priority. Then looking for a more peaceful job can come second.
Seriously, why do you stay in this relationship if it's so stressful?
If you like the outdoor life, how about looking for a job with the Forresty Commission or National Trust, or Warden of a nature reserve? Or perhaps working on a ferry in one of the Scottish islands. If you're looking for a job which gives you a lot of mental space, you will need to be a very self sufficient person. Are you? Or are you just looking for an escape from a nagging woman?