A phrase with different meanings to different people.
Best fit for me - A Fish
On the other hand, I may be classified as such by some from the past…or maybe that was “glad he got away” 
I don’t have one.
He was married before I even met him.
Define ‘relationship’. 
To me, the ‘one that got away’ is the one woman I was interested in, and with whom I thought I might have a chance with at the time I had the chance (as opposed to discovering much later). Sadly, I fell back from the chance, and it never came again.
They all got away. I haven’t even caught a fish in my life
The line broke before you got them in your boat. It could be a fish, or someone you thought you had a shot at, but it doesn’t sound like someone you actually dated to me, since someone you dated really was reeled in at one point, though maybe they threw themselves overboard or you decided to throw them back yourself.
I couldn’t vote. It means all of those to me, depending upon the context.
Previous thread on the topic. I remembered it because I am amazed at the number of people going for the second option. You have to have had a shot at the fish for it to be the one that got away. That fish at the other end of the lake, which you’ve not come within miles of? It didn’t get away; it never even knew about you.
Well in my case, it was this girl in high school. We never dated; I remember in jr. high my mother (of all people) told me that the girl had a crush on me but I dismissed it, although I wished it were true. Then through high school one or the other of us always seemed to be dating someone else, although we were good friends. At graduation she wrote in my yearbook “I always had the biggest crush on you!” :smack:
I moved out of town after high school, but ran into her at our 5-year reunion. We went out on a date and made out on her sofa, and the next day I flew home. She wrote me but I never wrote back because I was an idiot. A few years later she got married, which hit me like a ton of bricks. I’m now happily married as well, and we send Christmas cards to each other.
Although we were never in a relationship, she’ll always be the One That Got Away.
Someone you almost had a relationship with. Didn’t work out for whatever reason- one of you already in a relationship, long distance, etc.
For me it was Etta.
I disagree, and I’ll explain how I see the difference. The relationship one would be where you are together, but somehow things conspire so that it doesn’t work out, like they have to move out of the country or family gets sick. But in not having a relationship, it could be like those situations where you are friends with someone and secretly pine for eachother, but don’t realize it until situations make it impossible.
I voted the second option, because the “one that got away” I never really had a “relationship” with for much the reasons I mentioned. We had secretly had mutual feelings, but each thought that other didn’t feel the same and valued the friendship enough that it was fine that way. By the time it was made apparent, we had each accepted that state and tried to forge our own relationships instead, and after that point, either of us was pretty much in a relationship because waiting around for the other’s to fail is, well, a bad idea. At the point when we were both single and considering pursuing it, we had a very brief period together, as in a week or so, hardly a relationship, before other circumstances arose that made it impossible at that time. By the time that was resolved, as we both thought it was a bad idea to put our lives on hold and wait, we’d re-entered the previous state.
And that’s “the one that got away” because, just like that relationship where circumstances end it and the relationship never gets closure, I never had any meaningful closure on how it all went either. We’re still friends now, but it’s been years since that and I’m not hung up on it anymore
There was another for me at one point that I was in a relationship with before and circumstances intervened, but details later came to my attention that made me glad it ended when it did, so that one doesn’t count.
I’m a fisherman, what do you think?
For the metaphor to hold though, three things have to happen: You have to cast your line, thus expressing your interest. The fish has to become aware of your bait. Then it has to at least nibble at it, expressing its own interest. At that point, if you fail to reel it in, it’s gotten away. Before then, it’s just another fish in the ocean.
So, if you pine for someone secretly and never let them know, they’re not the one that got away, even if they are also pining secretly for you. Someone has to actually go fishing for a fish to get away. However, in the circumstances of the relationship you went on to outline, you expressed mutual interest, even if belatedly, and it didn’t work out. All of the conditions are met, and I’d say that one counts.