It is a truism that honesty has to be relearned as one grows up, because almost all of us are punished as children for displays of emotional authenticity.
Our parents or other authority figures often want us to feel differently to how we feel, so they punish us when we don't display the emotions they want to see.
And we learn this lesson deeply. So, when we are adults, we keep many parts of ourselves — especially those parts that we think are "wrong" — from others. This feels instinctive, natural, protective — we shy away from hurt, and so we must shy away from painful truths.
But dishonesty is a terrible way to squander a life. That truth which you hide inside of you, sooner or later, is coming out in some way or another. When the truth comes out, that never goes well. Sometimes it goes catastrophically bad. If you're hiding a wrongdoing through dishonesty, when people discover the truth, not only will they learn about the wrongdoing and judge you for it, they will additionally judge you extra harshly — yet fairly — for having misled them.
The converse is also true: honesty is a great life booster, as it simultaneously attracts honest people to you, and repels dishonest people away from you. You really want to have a life surrounded by honest people and with dishonest people as far away from you as possible.
And this is why we must learn to be honest again, first and foremost with ourselves, and then with our friends and family.
Remember: if people can't have you in honesty, they can't have you. And, most importantly, if you can't have yourself without lying to yourself, then change yourself.
Not everyone is capable of relearning it. But everyone is able to try.