relationship amnesia
forgetting that you are in a relationship and carrying on as if you were single
While dating someone for 2 years, Carrie occasionally had indiscretions and hooked up with random guys at bars. Guess you say she has relationship amnesia and forgot she had a boyfriend.
Relationship amnesia
When your S.O. Forgets how to do common things like booty calls, favorite sex positions, etc.
My gf didn’t know her favorite sex position anymore guess she developed relationship amnesia.