There can only be one truth.
Depends on whether we are discussing subjective 'true for me, but not necessarily for you' truths or objective 'true for everyone' truths. Clearly there will be many versions of the former, but presumably only one version of the latter. But your claim that you have a duty to evangelise suggests that you consider your god to be 'objectively' true - i.e. actually exists for everyone (whether or not they have realised it yet) and not subjectively true, in other words true for a believer, but not true for a non-believer and does not actually exist outside of the subjective belief of believers.
We cannot choose what is true
If we are discussing objective truths then you are correct, and that means that the truth may not be convenient, comfortable or easy.
- we need to use whatever means are available to consciously discern what is true.
Wrong - we should not use whatever means, but those methods that are objectively robust if we are trying to determine objective truths. So basing a conclusion on an objective truth on someone's subjective experience or faith is a very poor way to determine objective truths. Fortunately we have some exceptionally robust approaches to determine what is most likely to be objectively true - we call them scientific methods.
And we only have one lifetime to discover the truth.
No shit Sherlock. Why do you think I am a professional scientific researcher who spends much of his professional life trying to ascertain, using robust objective methods, what is most likely to be true. And although my contribution to new scientific knowledge, through my over 150 peer-revered papers, represents a teeny, tiny, tiny, tiny advance in our understanding of the truth, it is at least some contribution. Your contribution AB?