It won't automatically count against you. There's no rule in the UK that says autistic people can't adopt. I've looked into this a bit myself.
But they will have questions about it. That's not a bad thing imo. They're not looking for reasons to refuse to let you adopt but they'll want to know that you can provide a stable and loving environment for a child, that means you'll probably have to demonstrate that you can hold down a job (unless you're independently wealthy) and provide a home that's safe and suitable for a child. The fact you have a supportive family will stand in your favour. Given your diagnosis they'll probably have questions about your flexibility and your response to unexpected situations, that sort of thing.
If you decide to go ahead, good luck.
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It's dark. Is it always this dark?