Um, im not sure, but my understanding is that he came so much when they did it that it hurts when he pees. And knowing his personality, he's just saying he can't pee because it hurts a lot. I think.
He played too much with this part, while he wanted to cum (he couldn't do it on his own) and now it's sore.
╮(￣▽￣)╭
Thank you so much for the explanation ヾ(❀╹◡╹)ﾉ~ @AmanoChie
Thanks for the explanation ٩(๑❛ᴗ❛๑)۶ @roar
Could somebody explain to me why he can’t pee for the next day?