just fucked up lives in fucked up circumstances...
she was poor and needed money to support herself and her son. he was old, about to die, filthy rich, and horny. the 2 meet, and they were able to help each other.
she was unfortunate to have such fucked up "parents". and the guy was unfortunate to have loved ones passed away and needed something to fill that void in his life.
they actually do seem pretty perfect for each other. they were using each other if you want to put it that way, but isn't that how life works in its strange way?