BF and I were just talking about this. We both got married at 18 cause back in the day, that's what you did. Both had so so marriages for years and now that we are together, huge difference.
It was when we both realized that we would do anything for the other person without keeping track of what we did (if that makes sense). I think about his wants without resentment. We think about the other person with a smile and try to do things for the other person because we want to and not because we have to.