I've been around a long time. Long enough to think my changes had been made during H's crazier moments (you know the score; detach, GAL, mirror, etc.)
We've often heard that we don't cause their MLC, it's not our fault. A long time ago, and what I've quoted so often, is that we are part of a situation, and by changing our own reactions (the only ones we are responsible for), we change the situation.
Obviously I didn't cause my H's narcissistic behaviour. But perhaps I made it worse, by being too nurturing (an echo to his demands) and then too furious (which is narcissistic and causes a more narcissistic response by my H).
There is a better way; healthy narcissism, which means we believe we can succeed, deserve respect, etc. and don't get furious OR too helpful. I'm still learning not to get mad, and not to try to win arguments, and not to bend over backwards doing everything for him.