OP I would encourage you to ask yourself (a) what outcome you want from a situation, and (b) what you should do that would be most likely to get you that outcome.
I am also a truth teller by nature and folk hate it. Their responses to this aspect of my personality absolutely exhaust and demoralise me. I get where you are coming from.
However I have learned that "telling the truth" is not always the best way to get the outcome I want. So I now recognise it for what it is - just one tool in a large toolbox - and I strive to only use it when it will get the outcome I want.
E.g. with your friend being two faced. What did you want to have happen in that interaction?
Perhaps you wanted to trust her, and were genuinely asking her to explain what was different about you. If so -
Do you think that by asking her, she would respond with the truth?
I mean... she's already shown you she is two faced. You've seen clear evidence. So why ask that two-faced person to be honest with you? It was a fool's errand and marked you as naive at best.
In fact the better approach will have been to use the evidence you already have, to make a judgement on her honesty, and then treat her accordingly - i.e. just kept your distance, and your peace. In this way you do right by yourself and don't give the liar more of an opportunity to lie and dissimulate and later tear you down in the way you should have predicted she would.
You effectively walked up to a person who likes to tears others down, and gave her an invitation to tear YOU down. That wasn't what you intended, but the behaviour you chose got you that outcome.
Are you a person who believe that "truth telling" in and of itself is virtuous and therefore has to be the best course of action in all situations, regardless of the nuances? If so, you might want to examine that assumption and ask yourself whether it is actually serving you, or in fact giving others power over you when you don't intend it.
You have the power to exercise judgement in how you use your honesty. Honesty and assertiveness will not always get you what you desire from a situation.