|Firstly, I really enjoy the format you've used for this. In each stanza, the first four lines (ABAB rhyming scheme) feel as though the speaker is calmly speaking to the second person, as though they're trying to make sense of a broken situation. But in the last three lines (CCC rhyming scheme), it becomes rushed, more specific, as though the emotion is getting to the speaker, and it's rattling them. We see the personalities of both the speaker and who they're speaking to. It becomes more personal in the final lines of each stanza, and the power of the piece comes through more readily because of how you've set it up - well done.
This comes back to your description - this is something nearly everyone goes through. But everyone has their own experiences on the matter: what happened, what went wrong, how it all fell apart. And I think this poem does well in capturing that universal experience while also making it personal, bringing the reader into the speaker's shoes.
If I were to offer one critique, perhaps add another stanza that shows whether the speaker accepts that this relationship has passed, or if that "what ifs" are simply that. Something that could've happened, but ultimately may not. Something to close this off on - a theme or lesson, as they say. Answering the question: what is this poem trying to convey? Is it left ambiguous because the flow of time is ambiguous? But even then, there's usually some acceptance of the end, or perhaps a yearning to find out if these "what if" scenarios could come to life. Mostly just a suggestion to consider though :)