I think hypersexuality can definitely be a symptom of depression especially when other more common symptoms are present. It is much more likely that this was the case than that your ex was bipolar especially when the other common symptoms of that disorder were absent. Depression is in my experience with it in myself and others either an absence of emotion or an overwhelming sadness and hopelessness. I tend to fall into the latter when depressed and the urge to medicate that sadness, to escape it even for a brief moment, can be irresistible. You can do that with sex, alcohol, exercise, work or anything else that absorbs your mind and takes it away from its relentless focus on sad and hopeless thoughts. This is more common with atypical depression which can exhibit excess eating, sex, sleep etc . . . It is confusing because these symptoms are the opposite of those for major depression under DSMIV. By the way, I think you should focus on an important relationship that went wrong at least for some time precisely because it will teach you about yourself. Who we choose as mates and why we stay with them gives a person more insight about the self than just about any other activity.