I haven't had to have a stoma myself, but I have had bowel surgery that might have gone that way, I live with a lifelong bowel condition and I didn't want to read and run. I am so sorry to read what you are going through, OP, especially with the RV fistula etc.
OK, I know you want to think of the stoma as temporaryand maybe it is. We'll get to that. But even if it is temporary, you have to live with it while it is there. If you can't wear your old clothes because of the stoma, if finances allow get clothing that does work for youjust as you would if you were pregnant, or moved to Antarctica.
I also think you need to be honest with your GP about the effect the stoma is having on your mental health, your sleep, and your physical health. Stoma or no, temporary or no, you should not have to live in misery. Is there a UK equivalent of a stoma care nurse who can help you find a solution that means you will not be up and down all night emptying your bag? Sleep is so, so important for mental health, especially with an underlying condition.
Finally, if you can I strongly recommend looking for a way to live with the stoma. If the surgeon is not hopeful, you need to have a plan. Your GP could be a good help here. Your stoma care nurse could be. A support group for folks with bowel conditions could be. What is preventing you from working or having a relationship? Is it something to do with the stoma itself, or is it confidence? Is that thing something that can be ameliorated? Again ask your GP for help, here, and your local colitis charity--there may be resources you are not aware of.
I get it. Living with a bowel condition isexcuse the punshit. I have felt like you, wanting to die, never having a relationship, not seeing how I was ever going to have any kind of life. I really hope you can find a way through it.