It's not that song, it's a song that plays during the climax of End of Evangelion and has very strong themes of suicide and loss, played over an upbeat, lively tune. Just imagine these lyrics over something reminiscent of a Beatles song circa Sgt. Pepper's Lonely Hearts Club Band:
*I know, I know I've let you downz
I've been a fool to myself
I thought that I could
live for no one else
But now through all the hurt and pain
It's time for me to respect
the ones you love
mean more than anything
So with sadness in my heart
(I) feel the best thing I could do
is end it all
and leave forever
what's done is done it feels so bad
what once was happy now is sad
I'll never love again
my world is ending
It's one of my favorite scenes in animation, just because of how utterly fucked up everything is and how many layers there are to everything