I have something similar. My relationship with my ex-husband was 10 years long but it's the relationship I have the least baggage from and rarely think about. I had a very long time to process it as it was happening. I way overstayed and when I was done I was DONE. That door feels fully closed and far away.

Relationships that ended more abruptly, like my most recent one and my high school one, I still feel stronger about and think about more frequently. Closure is so important. Time helps but it takes many many years...