We met at 10 years old and are getting married at 24. When we really started dating three years ago, about a month in we did a spreadsheet of ~270 questions about how we wanted to live. We blindly answered so as to not concede or compromise in our answers. VLOOKUP and merge answers. 90% of them are basically identical. The remaining 10% are completely predictive of current and perhaps future points of disagreement and contention. All around it worked infinitely better than prior relationships. We assumed since we had been friends for so long that we could just build the love part. The byproduct of that has been growth mindset around resolving issues and making decisions that makes us extremely effective at helping each other achieve our goals and get our needs met by the relationship. I think a good litmus test for a relationship is how safe you feel talking about long term issues and resolving points of contention. If it just seems normal, invest there. If it is extremely hard to raise those issues, don't.