This has been something I've asked myself at times. Having become a brony 8 months ago I'd say I'm still fairly new to the pony phenomenon, but I can assure you that your obession is not unhealthy. In fact it's perfectly healthy. It only becomes unhealthy, like others said, if it begins to consume other aspects of your life and causes problems. As long as your able to go through your daily life, you are fine.