We have to choose our battles. There’s wisdom in Sun Tzu’s maxim of only entering battles that we know we can win. There’s also Lao Tzu who says (roughly paraphrasing), don’t be where the blade swings and you’ll never be struck. It sounds like your friend has already made their choice and therefore you won’t be able to convince them otherwise. Rather than tell them they’re wrong, show them they’re wrong by your example of your life and your love. You may not be the one to teach them this particular lesson. Maybe they will never learn it in this life. We all must make our choices, not acting is a choice as well. All of our choices have consequences. Being alive is consequential. What consequences do we live for? Only you can decide.