I'm very much in the "finish one serious relationship before you start on the next" camp. Just thinking about the logistics of trying to live a double life gives me a headache. I like that if my wife needs my phone for something, I can just hand it to her without a second thought.

My wife and I have geo-tracking on each other for emergencies. I think about it maybe once a year when I get a notification that it is on. I don't ever have to think about coming home and my wife saying, "Since when is your office located in [name district/street where my office is not located]."

There is the (dark humor) idea of "The Bonnie Situation" where I'm telling woman X that "I don't want to get fucking divorced" which was the idea behind my response in real life.

Mostly though is a lesson I learned late, but at least a couple of decades ago and not recently. If someone is willing to cheat on their partner with you, they will be willing to cheat on you.

I have a mantra since my epiphany a couple of decades ago and it holds 90+% of the time for any relationship: friendship, romance, business, etc. "The way a relationship starts is almost always how it ends."