Ake, I'm not convinced by your 'manic depression' theory, I'm afraid.   It's almost as if you think that sex with many partners is a symptom of illness rather than a choice (albeit a choice made, as all choices are, within constraints).

There are gay men with mental health issues, though my supposition has always been that prejudice against & victimisation of homosexuality play a very large role in that scenario. I don't think that even the most 'sympathetic' hetero can fully grasp what it is like living in a situation where simply being honest about a key part of who you are can lead to such damaging responses. Happily I don't face many of those hostilities in my current daily life, but I only have to read some of the comments in threads like these to know that prejudice is alive & thriving.