When I was in college, I had beenwas obsessed with western indie rock, b. Before that, western music had never been on my playlist.

"was" sounds more natural here.
Also, I think these work better as two sentences instead of one.

This March, an American indie pop band, The Walters, performed in my city, and suddenly I refindiscovered the enjoyment of western indie music again.

I think "rediscovered" sounds more natural than "refined."
Refined is more about skills than interests.

So, please let me go" have still occupied mey mind after the show.

I think adding "my mind" is better here since you are not physically occupied by the lyrics haha.

When I was During college, I had beenwas obsessed with wWestern iIndie rock, before that. Up until that time, wWestern music had never been oin my playlists.

You introduce this phrase by saying "During college." Since your time in college had a definite beginning and a definite ending, we would use "was" here instead of saying "had been."

Then II later discovered Franz Ferdinand, The National, and Lana Del Rey, to name a few favorite ones.

ButHowever, when I left college, somehow Western music lost its magic on me, and then. I turned my interest to J-POP instead.

This past March, an American iIndie pop band, The Walters, performed in my city, and suddenly I refind the. Going to their concert made me rediscover my enjoyment of wWestern iIndie music again.

So, please let me go" have still occupied me afteruck with me since the show.

This is a sort of figure of speech. We use "since" here instead of saying "after," because the lyrics are still in your head in the present.

Turn Tthe Radio Oon

When I was in college, I had beenwas obsessed with wWestern indie rock, but before that, wWestern music had never even been on my playlist.

Then I discovered Franz Ferdinand, The National, and Lana Del Rey, to name a few favorite ones.

But when I left college, somehow Western music lost its magic on me, and then I turned my interests turned to J-POP.

This March, an American indie pop band, The Walters, performed in my city, and suddenly I refind thediscovered my enjoyment of wWestern indie music again.

So, please let me go" have still occupied meuck with me even after the show.