Your feelings of envy are harming you by making it hard for you to achieve a degree of self-defined success that might lead to you feeling less envious.
The question is how to go about writing characters who aren't like you, not whether you are allowed to.
We often have to confront the undeniable fact that writing takes time away from other things that we, or other people, think we should be doing.
You have to pace yourself, like an athlete with an injury doing slow small exercises before returning to marathon running.
Work with your innate writing process rather than against it, and you'll be much happier and more productive.
Don't try to tell an "authentic" story. Instead, tell an "inauthentic" truth.
Critiques should not make you question the value of your work, or the value of yourself.
Let somebody else write only allistic characters. You can write a character who is probably, or maybe, on the spectrum, but this does not need a huge reveal or internal struggle—it can just be a thing you do, among other things you do, as an author.
The way you feel isn't a rational response to a defined situation, and can't be evaluated on that basis. Feelings don't stay contained and orderly. Some of your feelings may not even be about your writing.
Draw on the best of the way the world is and has been, as well as your most optimistic hopes for what it could be. The real world is very unfair to those on the margins. Use your writing to make up for it.