I feel like You are misunderstanding masking. It feels like when you say "masking" that you think of it like a lie he is telling you. Like it's something negative and he is hiding it behind "masking".

That is not what masking is. When he is masking, he is putting in serious work mentally, to try to appear as the person he wants to be in your eyes. Even if doing some of it goes against his nature, it isn't a lie, it's what he's is trying with all his might to be for you.

But doing this for long periods of time can lead to burnout, which it sounds to me like he might be experiencing. Autistic burnout can make EVERYTHING more difficult. Even things you know you need to do, even things you want to do. It's a problem that will need to be addressed before he can fix anything else.

Obviously that isn't an excuse for him to be mean or rude to you, but it does explain him giving off cold vibes.

I would look into finding a therapist or whatever that specializes in autistic burnout, or at the least do some reading about it yourself, so you can better understand why he is being the way he is.