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It will be very difficult to find similar stories around the web because your case is really specific.
What I'd concentrate on is that you have a history of pressure/muscular-related issues.

You mention RSI (I overcame that five years ago myself), and other tension related pains and strains. That's the first pointer towards a TMS personality. You seem, like many of us, to vent through pressure in your muscles.

So, why do I state the obvious? You kow what makes the vocal cords move when we sing and speak and even breathe? Muscles. Most promintent, the musculus vocalis is the inner muscle in the larynx. If it contracts, your vocal cords "close" the rima glottidis in your larynx. It works together with another muscle, outside, to create sounds. You say your doctors call it "muscle tension dysphonia". That is it. Your muscles are tense, and it puts a strain on your vocal cords. Thus, you feel discomfort and pain.

You can become accustomed to pain. You feel it, whether there's a physiological cause there or not. It becomes ingrained in your neural pathways. It's then that your first go-to reaction becomes pain.
It doesn't mean that you are damaged. Yet, that's the first thing we think. And it's crazy difficult to get out of that pattern of thinking.

A granuloma is most commonly found in singer's cords. But we are talking people who do this kind of thing for decades! On volumes you don't want to achieve in a non-professional setting. You "are not using them right". Well - usually, we know how to use our bodies. It's innate.

Your discomfort should've healed with rest by now, that's what most logical people would say.
You might've tired your vocal cords a bit, at the beginning. You felt slight discomfort. But then, you rested. Had therapy lessons to reduce tension and strain. Yet, no improvements?
Sounds fishy.

When we first establish a mental connection - cause and effect - between pain and an activity, that's where we begin to enter the dangerous zone of symptom obsession. It seems beyond our control, doesn't it?
I believe that we can put strain on our bodies. Tired muscles from working out, for instance. But that'll clear up. There's no reason not to, especially if there are no ruptures or anything observed!

Somehow, we enter a cycle. We try to protect oruselves by prescribing ourselves more rest than most doctors would do. To no avail.
It is scary, isn't it? The thought of never be able to use your voice again. Your arms, Go out for running. Bending, lifting.

That fear, that's the core of TMS, I think.
You don't sing anymore, do you?
I think it was an activity you enjoyed. It seems so, from reading your text. Yet, you had to give that up.
You gave up an activity that brought you joy and focused your attention elsewhere. Now, you can't hekp but forcus on this specific issue - your discomfort in your vocal cords. Some days, your life basically revolves around this and nothing else.

Your psyche is distracting you, and it chooses the most powerful venues it can find. Robbing you of your pleasures, instilling you with fear of crippling disability. I know this very well. This has been me, for so long. It's my go-to reaction to stress.
Negative thoughts. Overthinking your future. Anxiety.

You mention noticing how stressed out you where when you met your ex-gf. Why did you meet her in the first place after so long? Who suggested to meet up? She's probably a chapter you haven't quite closed but rather turned the page over before achieving closure. That's what I could think is causing some of your discomfort.
It might be a good idea to sift through your mind and emotions. What is causing you emotional pain - pain, that is so dangerious to your inner self that it prefers to let it out in physical form?

This is all I can say about it. I am struggling myself. I am sure that the body reacts to the mind. In some people, that connection is more fine-tuned, stronger. Yet, it's so fine we often overlook it. It's a two-way-street. And you can take the first step and recognize that we're a unit. I don't really think mind and body are seperate. It's one entity, working together always, and if one part is hurting, so is the other.

I wish you all the best.