I feel your pain, especially the challenges of trying to hold your
tongue and avoid saying something you will regret in the days or weeks
after an unwanted chop on your wife that took away years of growth.
But reading your posts, I notice a few things.
Your wife, who does not enjoy having very long hair, has grown it out
five times. Likely she did this for you. At least once it was to the
middle of her butt, and most recently it was to lower-back length. Many
guys here will never get to experience hair that long. You call it
losing the battle on the 5th attempt. I see multiple successes.
Most women seem to like changing up their hair. Unless a woman is a
true longhair, she's unlikely to maintain Rapunzel length forever.
Being with a woman who is at least willing to let it grow out for years
and have long hair sometimes is actually pretty good. You have
experienced multiple years of longer-than-mid-back length hair over
these growth cycles.
I assure you it would be worse for you if she kept trimmed to within an inch
or two of her shoulders for years at a time with no hope of it growing out.
Her being "repulsed" by your fetish is a shame, and perhaps something
you could work on together. But you're very unlikely to find a
therapist who will see her growing her hair to beyond classic length and
keeping it there to be a compromise. You're much more likely to find a
therapist whose idea of compromise is for you to be more tolerant and
your wife to not grow her hair out because the cuts are what upset you.
That may not sound like a compromise to you and me, but it might very well seem
like a compromise to your wife and the therapist.