Forgiveness and a Dropped Relationship

     How does one forgive another when one drops a long-term romantic relationship as if it were less than nothing? Truly, truly dropped it, as if it were truly less than nothing. The phrase "Less than nothing" is obviously not possible, because it is not possible to have less than nothing. That phrase was merely used to describe the severity of the dropping of relationship described above. How can one justify even doing that after twelve years of being committed to one person? It literally makes no sense to me. I do not use the word "literally" lightly. It truly, one-hundred percent, literally makes no sense to me. Perhaps it is the way my brain is wired, perhaps it is my environment or the way I was raised, but just dropping a relationship, nay, another person like that, is incomprehensible to me.
     As a man that holds on to anyone that I meet that I see as a good person, sometimes to my own detriment, dropping someone else just seems unforgivable and unjustifiable in any way. It just does not make sense. I have tried to drop people from my life in the past, even the ones I loved most. It did not work. After awhile I became less and less happy and I missed these people greatly. Eventually I made up with a few of them, and four years later, we are still best friends and talking almost every day, even though one of them lives in Florida and I in Ohio. This is why I cannot comprehend dropping someone, truly, truly dropping someone. Especially someone that this person has been with for so long. Do those twelve years mean nothing? Was it a waste of time? How can this person be forgiven, honestly, how can they be forgiven? That is the question. And I have no answer.