Has only happened once fully, but totally secret and very long term. I am prone to slight obsession about those I'm interested in, but I never approach them, I just wait. They never tell me they like me, of course, so I've learned how to let it fade and talk myself into believing they're no longer available and therefore no longer safe to be interested in. I guess they're merely lighter and I don't let them fully develop anymore. Relationships also die hard, usually taking at least a few years to pass sufficiently for another attempt.