this is where my mind went when i read the start,...
i reread the original post in it's entirety afterwards and while this post isn't quite what the OP is asking, it's just close enough to identify with as related

so one way to see what could be if things continued, or were closer and ... you'd be at the same place now, only the feelings would be many times stronger

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holding onto a relationship will create anger, bitterness and resentment

letting a relationship go before such negative feelings take over the relationship, you can still salvage love, compassion, friendship, ... it's just no longer a close intimate relationship.

things change at one time you two were perefect for each other for where each of you in your life, ... but as has been mentioned, we change & grow, if our relationship does not adapt, it's then holding onto things that are long past, the relationship gets sick, it's not allowed to breath, it's not maintained with love, it's now maintained with the past, obligation, duty, but no passion, no love, a commitment of a promise when you were, as you were before, not as you are now.

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please forget things & terms like "twin souls", these are madeup terms that glorify imagination, but have no purpose in reality, ... the best you can do for a relationship is to meet and fall in love with yourself, two incarnations of your higher self, who's incarnations are back-to-back, living together.

kinda strange way to look at things, ... but even then the progress of the soul from one life to the next, there is growth and development, to limit that so that one life can be happy with the next/previous life and think things are going to last, is insanely complicated beyond belief as you have to see both time changing to allow 2 lives to match up constantly, and the soul growing in both lives to reflect each individual life, ... a kind of exponential & zero growth all at the same time, ... be like watching the same repeat movie endlessly and enjoying it for 80 years, you know, so you can do it all over again with the next life.

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anyway, forget the twin soul **, it's fairytale imagination that has no bearing on reality.

you met someone that seemed so much your twin in all ways it bordered on fantastic impossibility, ... yet things grew, and changed.

one person wants to move on
one person wants to hold on.
one wants to work on things
one wants to move on
one wants to go back to what it was like before
one wants to move on.