You finally let your mom visit your dorm & like a typical boy, you didn't clean up. Unfortunately that also means she discovers a used condom on your floor. She doesn't get upset that you're having sex, she's just concerned about the lack of cum in the condom. Now she knows that your girlfriend isn't making you cum. Once she confirms that your girlfriend is certainly hot enough, she knows the truth about what's going on here: You can't cum for your girlfriend because you miss mommy's pussy. She says, "I told you that no other girl's pussy would ever feel as good as mommy's pussy, but you didn't believe me. You thought I was just messing with your head." But that's okay because mom missed your young cock just as much. "You've been saving all your cum for mommy, haven't you?"