Someone replied to one of his Instagram pics that they wanted to be with his 24/7 cheerfulness, and he replied he definitely wasn't always cheerful, but tried to see the good in things. The longtime friends who spoke at his funeral mentioned he was the one who would cheer others up, nothing about him ever being so down like you describe your bipolar friend and needing cheering up or hiding away from them (but maybe they wouldn't at the service. There certainly wasn't anything but one offhand remark regarding his homosexuality.) I also didn't pick up from his public posts much of any idea of boyfriends and break-ups, so maybe he kept all that private or had issues there.
Adam did have gaps in his public posts and it is possible he mainly posted good things publicly and others just to close friends, or he just didn't care to post that often, like many people. I saw one somewhat down post when he learned just after the 2016 elections that almost all his family voted Republican, but just said he was okay, just needed to trail run to try to help process that info. So still not convinced he was that up and down. His friends and family that he seemed so close to would know, I'd expect, but we'll likely never know.