In a monogamous relationship: would you be okay with your partner regularly going on one-on-one holidays that last more than 2 nights, like 5–7 days, with a platonic friend of the opposite sex — someone they had a brief romantic history with in the past?
There’s no specific reason for the trip (just a casual vacation), and this wouldn’t be a one-time thing — it happens once or twice a year, with one or two such friends.
Would you be comfortable with that, or would it make you feel uneasy?