I like to know why, too. I had an ex who broke up with me by saying he didn't have feelings anymore. He was about to be posted and we had fallen HARD for each other. The breakup took me completely by surprise.
His reason never sat right with me.
About a year ago, we got back in touch. He admitted that he just couldn't handle how intense things were and didn't want either an LDR or the guilt he would've felt if I came with him.
I remember feeling so relieved after we talked about this. I finally had closure!