Why is it the person you love the most can hurt you so badly? How is it somebody can tell you they love you and want a life with you and then the next morning tell you that he doesn't know about there being an us anymore? And why is it I feel pathetic that I have to go to a web forum to ask these questions?
There's an old saying, "You can only be betrayed by those you trust." Likewise, to be burned by love means you must care about the person. People break up for many reasons. Some good, some bad. A general fear of commitment, fear of being burned by love, differing goals in life, etc.
A while ago, I did exactly what your significant other did. I broke up with a very nice girl. I cared about her, very deeply. But, I knew our paths were not heading the same direction. She needed to do her thing, I had to do my thing. Eventually, it would not have worked. One of us would have had to make a sacrifice that was too high. I have no doubt that she was hurt by what I did, but I know she likely has long since recovered. I hope she finds someone with whom things will work out.
Your ex may have had good intentions, or maybe he was just being an idiot. Us guys typically are.
Hope things work out for you. Spend some more time at the range, good therapy.
