In Game of Thrones S3E2, Margaery speaks with the king Joffrey. He asks why she failed to have babies with Renly. She indirectly reveals that Renly was gay, saying,
"He had so many excuses, so many late-night war councils. He never wanted to try. Except one evening, after he'd had far too much wine to drink, he suggested something that sounded very painful and couldn't possibly result in children."
I guess she's referring to anal sex, but a male homosexual wouldn't want to have sex with women at all, vaginal or anal. So what's the meaning of Margaery's remark? Why did Renly suggest it to Margaery?