As a disorganized attached person who leans avoidant, one thing I recently learned is this:

An anxiously attached person feels regulated while they are in a relationship.

An avoidantly attached person feels a sense of constant dysregulation inside of a relationship.

So an avoidant will ALWAYS end the relationship eventually just so they can return to a sense of homeostasis. If they feel "unable" to end the relationship, they will leave by emotionally checking out, cheating, etc.

I'm trying to work through my attachment issues, but they are ingrained in me to a point that I worry it's impossible to undo the damage my parents did when I was a baby. Please know that we hate this about ourselves and wish we could just be happy inside a relationship like everyone else.