She tell him that he does not have to have sex with her. "But I want to", he tells her. "I enjoy it." "I'm afraid that you would try to get it somewhere else if you don't get it here." That isn't true, but he cheated on his ex and now feels like that is what is normal.
"I'm burnt out", he tells his mother. "She thinks we have to do it everyday before midnight."
She does not understand why he cannot tell her these things. Perhaps she will never know. Perhaps she does not deserve to know. Her entire life has been full of people loving her with everything they have in them, until they are tired of her and then they abandon her. She was born alone and has accepted that she will die alone.
She is not someone to love. She is someone to waste time with until something better comes along. Which isn't hard, since everyone is better than her.