I find this entire thread very interesting.
I am in my 50's, divorced nearly 5 years. I dated one man met via an on-line site for a few months but only a handful of times due to scheduling. We were exclusive because neither of us had the time to date others. We ended things kindly and still talk at random times.
I have dated two guys I met through friends. Neither worked out as romantic partners but we are still casual friends.
Then there have been two long-distance situations. One was a casual thing. Friendly dates when we had the opportunity. He introduced me (fix-up) to a friend. Friend and i dated for over a year...talking daily, texts multiple times daily, traveling to each other at least once per month. He brought up long-term, permanent plans and goals for the two of us. Discussed where we would reside together, etc. We had met each other's friends and familues. Until I overheard a bartender in his town ask "is that your girlfriend?" "No, just a friend".
Sometimes even when exclusivity is stated, the meaning is different between two people.