I have a friend who also is very much subscribed to the idea the truth, reality, and morality are all relative. The irony I have discovered in this is the idea of saying truth can't be discovered, but that only concrete evidence will convince the person something is real. The irony also that while they won't subscribe to a religion, it being "unproveable" (I disagree about this), they are happy to believe in relativistic philosophies, which ARE unproveable. Your friend's attitude is unfortunate. To me it boils down to not wanting to know. Congratulations on speaking up and trying. You opened your mouth, and that's what is important. My hope is that one day something will happen and your friend will not just want to know if what you told him is true, but will need to know. Faith, after all, is not simply an inner belief without evidence. Alma and Amulek taught that it is real knowledge based on positive results to experimentation, nurtured with patience and diligence into a very real understanding of truth. In other words, hearing the word of God and acting on it. (As my mission president once taught, leaping up out of his seat from where we all thought he was asleep). Would it have been faith for David to believe with all his heart that God would defeat not only Goliath but the whole Phillistine host, and then he turn around and refuse to fight? Or run, as he did towards Goliath, slinging stones but not believing he had a chance? No. You wanted to know the truth, you did what God directs to find it, you asked, you received. One day perhaps your friend will do the same.