I think we need to reevaluate the length of Sage's relationship with Chad. We assume it's nearly two years old because Sage was clearly smitten with Chad in the Episode 5 flashback, but consider this line from Episode 8:
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I think it's more likely that Chad spent a long time turning Sage down, and only accepted (rather suddenly) when he felt like he needed an official girlfriend for some reason. If so, there's a good chance Chad needed a beard coincided with whatever happened to Troy. Troy was still with the Jocks in Tommy's story of him fucking Arieth, which was "a year ago."
So I'd say the relationship between Chad and Sage lasted at most ~1 year, and possibly less. It's still way to long for him not to have mentioned that he was gay, but it does make Sage's dry spell a little less egregious.
Eh, it seems fairly straightforward to me. As Sage says, she wants to stand on her own two feet, and as a result has developed a habit of simply refusing help from her parents. It would make sense that her parents responded by INSISTING on helping her, which in turn convinced Sage to avoid interacting with them as much as practical to minimize their opportunity to insist. It's a sort of vicious cycle of virtue.
Ehhh, I'm not seeing it. I could easily see Troy sending the pics to Dawe if he somehow had access to them, but I don't buy that it's as easy as hacking Arieth's phone (since she didn't take most of the pictures). And I guess I could see him sending a letter to Chad in the hopes of convincing him the secret couldn't be kept so he might as well admit the truth and leave the closet.
But I can't see him sending both letters together. It maximizes the chance that someone else might open Chad's letter, which would be disastrous. It would also maximize Chad's effort to figure out who sent the letters (which would be counterproductive from Troy's perspective) while minimizing the chance Chad will get introspective about how viable the secret is (which IS what Troy wants).
So I'd say Troy is just about last on my list of suspects for the letters at the moment.