[quote=@Birdboy]
Looking for some advice on how to portray these sorts of things without coming off as overbearing or like I'm seeking pity for my characters. I general, to any people here who [i]do[/i] have disabilities of any kind I would love to know about any things I should know about portraying your specific needs or perhaps things I should avoid doing. This goes double if you see it often.

The character I'm trying to portray is someone with selective mutism, but has been thrust into a situation without any of their usual support group. I imagine they might manage to open up to a few people in small burst when alone.

Advice on playing a character that does not speak in general would also help me here, but I figured I might broaden this conversation for a better dialogue and to perhaps learn something as I go.
[/quote]

If you're not seeking pity for your characters, don't. Selective mutism would be an aspect of them but they would have many, many, many, many more sides and capabilities to them than this. 

When you're writing someone with a disability, are you making it all that they are and the only interesting thing about them? I have a disability irl and it is absolutely by far the least interesting thing about me. That said, it's part of me, and it's not something to be "cured" - same would go for characters with disability unless you're writing from this angle as part of acceptance of the self/character journey.

I've written a character who was blind, a mute character, a character with chronic pain and amputation. While the disability played a part of the character and their perspectives of the world around them, they had so much more than that to offer the roleplay.

Agree with what others have said about using expression to your advantage in regards to the actual writing. Otherwise, it's fictional - it's your world and you can do what you want.