Worried about my future career progression? What can reduce my anxieties?

Ok so I've been working for the same place for over 5 years now. I feel like I've learnt a lot of different tasks but these are all the tasks which I have picked up because it is always done in the same way. There is a step by step way of doing it overall. I have written my own step by step notes, screenshots to help me just in case I do forget how to do a task if I haven't done it for a while. I really struggle with tasks which are not done in the same way, grey area tasks and also tasks where you have to read between the lines. I get on the job training but I can never pick up on how to do these tasks no mater how many times it has been explained to me by my line manager. All the tasks he taught me if there is no grey areas, reading between the lines, the task done in exactly the same way, I noticed I understand and pick these up on how to do these tasks very quickly as long as it's explained to me 100% precise and clear as possible with step by step notes written by myself while being taught.

A new person will be starting soon and he is a similar age to me. I am meant to train him in my tasks as well and my line manager said he'll train me and the new person to progress further. He is just a bit below me because he is new starting. I will still be doing roughly the same tasks I have always been doing for 5 years but he'll be first call to do one of the tasks which I won't have to do and I'll have extra time to do my own assisting tasks.

My worry is, because he doesn't have my problem, I feel like he'll progress way faster than I will and I feel like I'll be his assistant in no time at all. I really don't mind being assistant and doing assistant tasks at all it's just the worry and disappointment I feel in myself for have 5 years extra time than him and he's already learnt everything way faster than me and I kind of feel like everyone in the workplace will know and I won't know what they'll think about me because of this.

What actions can I do to reduce this anxiety? I really feel kind of lost and trapped job wise because of this situation, when I get taught new tasks, it's either I get it, or I don't get it. And I noticed with some tasks that I've been taught, if I don't understand it, I never can understand it no matter how hard I try to. I find that this applies especially with tasks that have no rules, step by step way of doing it, I can't take notes down because it's done differently every time and my brain just can't process it. I feel that this is a disadvantage to me to be able to progress further. Is there any way to help with this? I know it will be very difficult because that is how aspergers effects me in a big way. I was thinking if I end up not progressing, I will leave this job but it's so difficult to find another job I had to really try very hard to even have this job what I got now.

I suppose another idea would be to start from scratch if that happens and learn to start a completely different career path that have jobs that are done in exactly the same way every time. No grey area tasks at all to learn. But I fear doing this because of money and if it will even work out in the end. Plus with these social understanding difficulties, it really tires my brain out a lot (as it did when I first started my job that I am currently at) to learn every single thing, I'll have to write everything that's being said to me down because if I don't, when I listen to tasks being explained, I notice I am trying to process that part of the information and I find it difficult to remember the last part of information that was being said.

Or would there be any way to discuss this with my employer? Would there even be any work adjustments which can help? I don't know what can help solve this problem overall because grey areas/reading between the lines has always been a struggle for me and I know it will just stay that way, probably ways to reduce it but I don't think it'll be ever completely gone because of how some aspies brains are wired I guess?