This is an interesting question. I've wondered it to about myself. I did the same thing with music like you did. I also became an Atheist. But my examples also went further than that. I had a friend who was really into photography, so we would go out and shoot and I really enjoyed it and had all these artistic ideas and everything, but now we're not friends and I don't remember the last time I took a picture.

Growing up my dad was really into sports and we watched sports religiously for most of my life and I got caught up in all that "passionately" as well. But again, now that I'm on my own I could really care less what's going on in the sports world.

I'm in my late 20's now and throughout all my prior "changes" some things stuck with me, some things didn't. I still listen to the same music I got introduced to by my friends and I'm still an Atheist. The way I've sort of explained it to myself is that it's about adapting. I mean, that's a normal thing that humans do. We adapt to change in our environment. And that's what I think I did. A new person came into my "group" and if I wanted to remain in that group I needed to conform. It was never a conscious thing I was never intentionally "selling-out," but I think it's inevitable. It's simply how we are designed. Things can appeal to you for different reasons, but sometimes things simply appeal to you because they are advantageous.

Now I feel like I do have my own identity, but it could very well be because I've had a pretty stable life for the past few years now, so maybe I just feel like I've found my place.