I'll admit when I first read this I though it was BS until I thought about my years of running in college and it seemed to make perfect sense! The best year of my collegiate running career perfectly coincides with with the breakup of my long term girlfriend. Ran all my PRs junior year right after we broke up.
Meanwhile, the girlfriend ran horribly after the breakup going from top 3 on the team to bottom half before being injured the rest of the year.
Started dating a girl senior year and my performances declined never approaching my single, junior year PRs again. How I wish I could go back with this newfound magical knowledge now...