Gf (25F) says she has not been happy in our (24M) relationship, and feared to tell me We've been dating for a little over 1 year and gf just shared that she has been unhappy but feared to tell me. When I asked why she feared this and why she's been unhappy, she doesn't have an answer.

Until now, everything has been going great, now she flew away for Christmas holidays, and we haven't seen each other for bout 10 days and she shared this. 

She doesn't have an answer on why she is unhappy in our relationship or why she feared to tell me. What am I supposed to do? How can I help her? I asked and she said I can not help her.

How do I deal with something that is not in my hands, but inevitably, it also seems to be my fault? As I never realised that she was unhappy or feared me in any way?

Tl:Dr; Gf says she has been unhappy in our relationship and feared telling me, but doesn't know the answer to either. Did I fail in detecting this and can I do anything to help?