Yui – Good-bye Days (English Version) lyrics

Overall, I think this song is about someone who has fallen in love with a close friend, but never found the courage to confess their feelings. The lyrics, "if only I could say 'Yeah, hello! My friend', with a smile," obviously implies that the singer and the person they are talking about are, well, friends. Also "I pass one ear phone over to you", shows that these two people are close friends because they do not mind sharing the same pair of ear buds and getting physically close together.
So now we can easily assume that these two people are friends. Now we can look at how the singer feels towards this person. The lyrics "if only I could say 'Yeah, hello! My friend', with a smile," and "An uncool kindness is at my side with you," shows that being friends isn't enough for the singer. We can also tell that the singer is extremely reluctant to confess their feelings, implied by the lyric "Can you really love me?" Also, the lyric "If possible, I'd like to not have sad feelings.
But they'll come to me, won't they? " implies that the singer is fearful of rejection, but I also believe that it could mean that they went through their whole life without confessing their love, and this becomes evident near the end of the song. "I wish for you to be by my side, I'm glad that we were able to meet each other, with such an uncool kindness. " The part where the singer says "I wish for you to be by my side, " implies to me that this could possibly be taking place sometime in the future, where the two people are no longer friends. "I'm glad that we were able to meet each other, with such an uncool kindness" implies that the singer still loves their friend, but this time, the 'uncool kindness' shows that the singer never revealed their true feelings. I also feel that the title, "Goodbye Days, " represents the remorse of never confessing your love when you had the chance.