I think we can all tell why he 'wouldn't tell you' if he was gay - you sound over-involved and unhinged!
His friend has 'been in his bedroom'?! WTF, OP?!!
Get your beak out AND understand that some people, gay or straight, don't meet their life partners at 17 and settle down and start pumping out kids!
I for one was TERRIFIED as a young person of getting trapped in my small town. I avoided relationships, had an abortion when fell pregnant and ran from that town at the first opportunity, truly feeling that i never wanted to be a Mother.
I met my other half and settled down at 36. I used my absolute right as a human being and changed my mind about having kids BUT if I hadn't it wouldn't have been anyone else's damn business.
I know for a fact some of my small-town/small-mind extended family members assumed I was gay because i holidayed with my female friends. What was i supposed to do? Never go on holiday?!! Absolutely ridiculous.
Leave your nephew alone, FFS.
Your opinions on his life mean NOTHING.