やるせない

"The Japanese have words for sadness that are so subtle and complicated that the English translations don't do them justice.
Setsunai is usually translated as 'sad', but it is better described as a feeling of sadness and loneliness, so powerful that it feels as if your chest is constricted, as if you can't breathe; a sadness that is physical and tangible. There is another word, too - yarusenai, which is grief or loneliness so strong that you can't get rid of it, you can't clear it away.
There are some things like that. You get older and you forget about them, but every time you remember, you feel that yarusenai. It never goes away; it just gets tucked away and forgotten for a while."
...
"The day after the funeral, I checked my company e-mail account, something I rarely did. I had an unopened e-mail from Hamaya.
It was sent about two days before she killed herself. I have never opened it. I've never had the courage. I don't want to know. I think I have a copy backed up on a hard disk somewhere. I'm not going to look for it.
What's yarusenai?
it's that one e-mail you never replied to and will never open. It's the bad advice you gave and the phone call you should have made and everything that came out of it. It's thinking about the friends that you suspect you might have been able to save."

(Tokyo Vice, J. Adelstein, 2010)