Not ones where you fell out but maybe ones that were at a certain time or in a certain place.
My contribution is a girl I met whilst working in a city in Spain. We were from opposite ends of the country, different cultures but became absolute best mates for that month. Aimed to meet up when we got back to the U.K. but it never happened and eventually we stopped messaging. I think of her fondly though, and the crazy amazing time we had.
I have another emerging one with a mum at school who I hung out with nearly every night after school when her husband was away. Long summer evenings in the park with our daughters, each saying 'we'll go in a minute.' Now it's too cold, she's moved and her husband has come back and it all feels different already.