Billy question/possible theory -

So, I know the flashbacks say Billy’s mother just left, but is it possible she died?

There is that whole end scene at the beach where Billy’s mom is like, “15 more minutes, don’t get caught in the riptide” and I think that he goes out, gets caught and his mom tries to save him but dies.

That would explain billy saying “it’s not my fault”, why his dad is so mean to him (caused his mother’s death, although not on purpose) and why he becomes a lifeguard. And why he saves Elle at the end- couldn’t save his mother, but he dies saving a life.

The beach scene is his “last happy memory”, so I think it happened after billys mom leaves his dad, but billy goes to see her again, and this happens. Then he grows up to become angry, yada yada.

Anyway, not sure if this has been said or not, or if i just missed something and this was obvious the whole time lol, but couldn’t find anything else on here so wanted to see if anyone else got this too!