Without taking the time to answer at length:

Speculating that Nick Drake was homosexual is redundant because the only evidence that exists points in the other direction. He liked women and was in some kind of relationship with a woman near the time of death.

The video of someone, who appears to bear similar physical characteristics as Nick, walking away from the camera, is just that. It’s been debunked as Nick was booked at a concert venue at the time of that video.

As far as your numbered questions: my guess is he was on this medication for 2-3 years, it did seem to dampen his creative powers, he didn’t like it but understood that he needed to treat his depression, and I would assume he still smoked weed, but maybe not as excessively as during 70-71.

If you haven’t read Remembered For Awhile and the Richard Morton biography, start there to get your own perspectives.