Thank you, SammysMom, for your directness and encouragement - and all of you. So many of you have succeeded where I've feared to tred, it's undeniable that there's a way, if there's a will. And there is.
Yesterday, I went to a wine tasting event in the countryside, and beside it, incidentally, was a paddock with 2 beautiful horses grazing and enjoying each other and the sunshine. As everyone buzzed on enraptured about wine, cheese, yatta, yatta, all I could do was gaze over at the horses and dream of "what ifs". My husband said that had they been male humans, we'd have a big problem!
After a few hours of this, I could stand it no longer and finally got up and walked over, as I'd spotted their owner in her garden. She allowed me to visit and snuggle to my heart's content, just for the asking!
She asked me if I rode, so I gave her the social version of my situation - where I try not to sound devastated, lovelorn and pathetic. She told me she knows many people who have similar tales, but, quite simply, if you love them and your soul needs this, you find a way. I'm not a big believer in coincidence, but I think I was meant to hear that message, unadorned.
Today I went to the beginning of this thread I started in some despair and re-read the whole thing. I thought about how much time I'm spending on what makes me sad, as opposed to pursuing what makes me happy. I need to do everything you've all said: yes, lose the weight, do strengthening exercises and tell (not ask) the trainer I need to mount from a block -at least for now.
But also, pursue what I love, with confidence, as you do.
I'm going to sign up for that introductory lesson and ride with another trainer and seek an objective evaluation, and if my own trainer can't see her way clear to work with me as I am, right now, I must find another who will. The only way I will stop is if the horse tells me to, not my own insecurity - and not anyone else.
If you love them and your soul needs this, you find a way. Full stop.