This is what we do

Accident.

Listen. Harry James Potter was an accident. 

you cannot convince me otherwise. Lily and James were 19 when they got pregnant, there's no way that was on purpose.

please, picture it.

Lily tells James they're pregnant, James panics, leaves finds the other marauders and demands a lads night out, you know, for no reason, just some drunken shenanigans for no reason at all  with friends. Remus notices something seems off and keeps an eye on his friend, but no one says anything. it's only several hours later when James is drunkenly sobbing on the toilet floor, "he's going to be so SMALL !!" that they realise what's going on, they ask him if he is going to be alright. he sobs, tears running down his face he nods, furiously "this is the happiest I've ever been!!" the other look at each other and pull him to his feet, Sirius marches him back home to Lily who has been waiting, scared, alone and a little bit more pissed off at her boyfriend for the best part of the night, she softens when she sees James drunkenly leaning on Sirius, Padfoot shrugs in apology, because James is a mess but at least he's at home now. James falls to his knees in front of her and says "I'm so sorry I ran off I got scared, I'm still scared, but I'm happy too!!" Lily can't help but smile "it's alright James, we'll figure--" but James loudly shushes her and points to her stomach "Wait I'm talking to my son" Lily glares at him ad reminds him it could be a daughter. Sirius adds "could be twins ! or quintuplets !!" Lily glares more and tries not to laugh while James murmurs into her belly " M gonna ask your mum to marry me, but keep it a secret 'cause I have to buy the rings first, and a broom, not for the wedding, for you, do you like quidditch ?? you probably don't know what that is yet. don't worry. I'll teach you. I'll teach you everything...