I'm looking for the name of the artist who sang an obscure song from the early eighties that I believe was called "so long".   I believe the artist's last name might be Fritz or Fitz but I'm not sure.  Some of the other lyrics in the song are "why didn't you tell me" and don't leave me this way".  Your help is appreciated.  Thanks.

Could it be this one:

Fischer-Z - So Long

When I read your letter I couldn't believe that you'd gone.
I dialed your number but no one answered the phone.
I asked your friends to tell me if they knew where you were,
they said they thought you were ill.
I hired a detective to try and find out where you are.
He managed to trace you, I know that you are living in France.
A watchman saw you climb into someone else car and drive off
laughing in the night. Why didn't you tell me? Not leave me this way.
You should have warned me and not waited for so long.

I've tried to forget you but I find myself walking on the street.
I went to the doctor and he gave me something to sleep. I've sent
you telgrams but you haven't answered one. Your mother told me
I best leave you well alone. I hope you're satisfied now you've done
this to me. I hope you're pleased with what you've done.
Why didn't you tell me? Not leave me this way. Oh you could have told
me and not waited for so long.

For so long I never realized just exactly who you are. I never
realized just exactly. I never realized the girl I had before.
I hope you're satisfied now you've done this to me. I hope
you're pleased with what you've done. Why didn't you tell me?
Not leave me this way. Oh you should have told me and not
waited for so long.

I love that song.  It's included on New Wave Hits of the '80s Volume 2, one of the best of the 15.  :)