I'll acknowledge that I speak from a privileged position, but from up here in my ivory tower, I can see that a lasting relationship is necessarily founded on trust.
Sometimes in life we develop defense mechanisms that are self defeating. I bet a lot of us are familiar with the conundrum of the IT department that always says "no." The environment becomes too constrained for work to be done, so the rest of the business develops shadow IT out of necessity.
Telegraph to your partner that it's unsafe to discuss their friendships with the opposite sex with you, and they will start hiding that information from you.
But I envy you living in a snowflake world without insecurities, cheating, divorces, etc.