You haven't changed. You may say: 'I'm full of love, I'm full of truth, I'm full of knowledge, I'm full of wisdom.' I say: 'That's all nonsense. Do you behave? Are you free of fear? Are you free of ambition, greed, envy and the desire to achieve success in every field? If not, you are just playing a game. You are not serious.'
Perhaps there is no other knowing than the mere competence of the act. If at the heart of one's being, there is no self to which one ought to be true, then sincerity is simply nerve; it lies in the unabashed vigor of the pretense. But pretense is only pretense when it is assumed that the act is not true to the agent. Find the agent.
As for the search for truth, I know from my own painful searching, with its many blind alleys, how hard it is to take a reliable step, be it ever so small, towards the understanding of that which is truly significant.