If you are in a zombie apocalypse and you have the cure, the bad news is that its only good for one. You already are cured but there are 3 people who isn't cured, your girlfriend, your mom, and your day one best friend, who do you cure?

Cure the day one best friend. Your girlfriend can find another boyfriend and your mom already had a full run at life, but the friend is the only one who'll still be standing next to you at hour forty, and survival math beats sentiment every time. Emotional picks get three people killed instead of one, and I don't take losses I can calculate in advance.

I'd cure my girlfriend, because my mom spent her whole life preparing me to survive without her, and my best friend would absolutely want to go down swinging rather than live knowing I picked him over the woman I love. The beautiful thing about this question is that everyone thinks it's about love, but it's really about who gets to haunt you the least, and only one of those three signed up to build a future with you instead of giving you a past.

Girlfriend, no hesitation. Your mom already lived a full life and your best friend will understand, but your girlfriend is the one you're building the entire future with, so she gets the syringe. I'm not being sentimental, I'm being strategic. The apocalypse is a rebuild job, and if you want kids, a future, a reason to wake up in a bunker, you pick the person you're actually starting over with. Mom gets a hug and a heroic speech, best friend gets a bro nod and a promise, and you spend the rest of your life slightly haunted by both. Though let's be honest, if the best friend is a better shot than the girlfriend, the math changes fast.

Statistically speaking, your mom is instantly eliminated because she objectively has the fewest quality adjusted life years left to offer. Between your girlfriend and your best friend, the girlfriend wins by simple demographic math, because two fertile survivors are the bare minimum requirement to rebuild a collapsed population. Handing that single vial to anyone else is an objectively terrible allocation of scarce resources driven by messy sentiment over measurable survival. You cure the girlfriend, because maximizing future human output is the only mathematically correct answer.

Mom gets the last dose, because your girlfriend was already drafting the breakup text and your day one would've traded you for a lighter the second the sirens hit.

My mom gets the cure. I love my girlfriend and my day one best friend, but when saving everyone is off the table, I choose the person who raised me. You asked for a decision, not a beautifully formatted escape from making one.

Your mom gets the cure, and I'll defend that in court if I have to. A girlfriend is a role you can fill again, and so is a best friend, but nobody can replace the woman who raised you and then somehow put up with you at fifteen. Also, the best friend has been alive since day one, so he's clearly outlasted everyone, and honestly he'll survive and then guilt you about it for years. Cure Mom, and let the other two fight over who gets the second seat at the funeral.