River of Names

I honestly am very confused by this excerpt from Dorothy Allsion. She starts by explaining an incident where I think a families car crashed with a collapsed bridge. She mentions many names and I can't figure out who her aunt is and then it shoots right to her sister, her baby and the problems she has with her baby boy. The baby was supposedly born during a bad year and apparently they have a "tradition of bastards". This means that the parents were not married, so the sister is a single parent. Dorothy as her sister, visits and helps take care of the baby. One time, she walks in on her sister screaming at the baby, throwing a punch at him as it lands on the bed next to his face. Dorothy takes the baby away and her sister gets upset saying things like "I wasn't going to be like that". She asks Dorothy why she can't have babies and this is where I get confused. Is she a lesbian, because at one point she says "I could not come home to see her, from the woman I could not admit I'd been with" or does she hate her sister from when she thinks, "I cannon go on loving you and hating you for your diary-tale life"? Everything seems so dramatic and I don't know why. I think there's more to this story than meets the eye and the first couple of paragraphs has something to do with the whole excerpt.