I can very much relate. I have tried to force my brain into positive mode. Sometimes i am successful...sometimes, not so much. We have had quite a few dates tank due to wandering thoughts.
Maybe one thing you can do is to think of one really great, epic moment in your R journey. something that, regardless of the A, takes you to a very happy place in your mind. Maybe its a date, maybe its a specific act your WH did, or a gesture that meant the world to you. Write it down and carry it with you. When you need the positive reinforcement on those kinds of days, pull it out and read it. Let your mind go to that place instead.
hugs to you!