This song (後悔: こうかい, koukai, "Regret") gives a feeling of what I often feel, despite my life not having much in the way of giving my heart to others (as the lyrics do).
To be honest, I prefer the cover more. Unfortunately, I couldn't locate lyrics.
I do realize that I've mainly been putting stuff up that's been done by this same artist, but those songs are what I wish to put up. When it seems right, I'll share other artists from my collection.