Obviously, after something like that, Andrew and Maxwell's plans were interrupted.
Maxwell wanted to continue, even begging and pleading with Andrew that he didn't mind, and he could knot him as much as he wanted, his eyes filled with lust, but Andrew wouldn't have it. After the second condom broke, he was worried. He was especially worried since it had felt like he'd ejaculated twice the amount that he normally did when he came, so it was basically like he'd nutted in him four times.
That was scary for Andrew, and he knew that Maxwell was trying to make light of it because he didn't want to worry him, but Maxwell should be worried too. Andrew wasn't an idiot. He'd heard the story.
His father had only had to sleep with his Mom one night, and Andrew was conceived. It wasn't a far stretch for him to think that these actions could result in a baby.
