i think it must be remembered that it is fiction, it is a story, and the stress in that world is not your own. it's easy to get caught up and put so much of your feelings into your character and vice versa- but in the end, even if things go poorly, you can play a new story with that character, can't you? write a little fic for them on your own, a fix-it or whatever you want.
but in terms of communication: you do not have to express yourself perfectly on the first try. if you are not clear or people misunderstand, just ask them to pause and let you clarify. work together to figure out how you each can make things clear to the other. nobody ever succeeds in expressing themselves with complete clarity to every person in every conversation; so much of interacting is just figuring out what the other person is saying haha. you just have to keep working at clarity until everyone is on the same page. it's fine! it you're really worried about it though, writing it down a few times in a few different ways can be a helpful way to figure out the core of what you want to express- then even if your words get off track while talking, you have those core ideas you can keep circling back to.