Woman discovers her stepson masturbating and fucks him

Three years ago this woman married a widowed man who had a child. They moved in together and since then she has had a very good relationship with both of them. The young man has grown up and is now a teenager about to leave for college. One afternoon the two of them are alone and she goes to the bathroom, but before entering she realizes that there is her stepson masturbating. She thinks about scolding him, but he gets so excited that she can't tell him anything. He stays there listening to the sounds she makes and she starts masturbating with her fingers too. The boy listens to her and fucks her in the bathroom before his father arrives and discovers them.