It could also be a mental thing. You already know what MDMA feels like, you know what to expect etc. But this kind of things happens to almost any event in your life. But that doesn't mean you have to give up on MDMA.
I remember the first time I traveled to NYC, I felt like I was in a movie or something. Everything felt so incredible and new. It was almost like I was tripping or something. Just going for a walk around my hotel was a whole experience in itself. Seeing the Rockefeller center, Empire State Building, Grand Center Station, MOMA, Central park with my own eyes made me feel like I was in a dream. I remember when we driving from JFK to Manhattan, I felt like I was transported into a GTA game. I never realized the the radio in the states was really like the radios in GTA.
But once I moved to the US, I would visit NYC at least twice a year and this feeling of wonder and excitement never really returned. However, I still enjoying visiting NYC and I've learned to discover beauty in other parts of the city such as Brooklyn and Harlem.
I think there are parallels to discovering/experiencing MDMA and my own experiences with visiting New York. I'll let you come to your own conclusions.
P.S. Yes, I do love New York, if you haven't noticed!