Why is it that guys have an easier time getting over a girl they went out with?

I have had a year to recover from the guy that dumped me, and I truly liked him. So, I have had a hard time getting over him, and it doesn't matter what do to help it, nothing helps. I have tried everything and anything to not think about him. From getting involved to talking with friends, going on walks, and even working on my grandmother's garden. I can't even sleep at night, what else can I do? Should I get a dart board and start throwing darts at his picture?