My first was a true, random stranger, a chance meeting in a hotel sauna late one evening. He was there on a stopover as flight crew. After a few minutes of conversation we just clicked and it all happened. Maybe I was lucky. That was 15 years ago, no regrets.
I've tried various apps over the years. I now use just two, fabguys and fabswingers. Through the latter, I've discovered a bi club, where we meet twice a month, and I get all the action I need. Have also ticked off the bucket list a few of my fantasy group scenarios.