Think about it in a different way. Suppose you talk perfect English from the start. "That nativee speaking guy will be like "What the heck is happening? Wasn't I supposed to talk to a non-native speaker? Where are all the mistakes? This girl must playing tricks on me. She obviously doesn't need my company to improve her English. Gosh, she may be even speaking English better than I. I'm leaving..."

  Perhaps you should  work toward lowering your expectations, and   decreasing that

"heightened sensitivfity" you have developed  about a  language partner.

  If you adopt an attitude which assures you that you are only searching for  at least one language partner that can lead you  and guide you into relaxed and comfortable language pracitce, your  activity will be more   pleasant and less stressful.

    What you are doing can be described this way.  You are giving away all of your power to  others.

That is not necessary.  Your partner is just a person   offering some language practice.

They aren't "God".  They are just people.  Nobody has to be perfect. If someone is not friendly with you,  or if they seem unkind,   forget them and look for another language partner.