Get thee to a psychiatrist ASAP. You are playing with fire and are apt to get seriously burned. But you need to realize that impulsiveness related to bipolar is one thing; a full-blown affair that's lasted a year is not impulsive but deliberate. Even if it turns out you are bipolar, you can't blame it for all bad behavior---you are still responsible for your actions.

Please, if you care about your marriage at all, end the affair NOW and get into couples counseling with your husband to work on the issues you've mentioned here. Best of luck.