What happens when you have a bacterial conjunctivitis on one of your eye but you closed it for almost 3 days, will it cause serious side effects on it once you open that eye that you closed for 3 days? it's bacterial bcs my eyelashes becomes crusty?

Your two eyes share an indirect connection through the tear ducts that enter the nose. I would not consider what you did as totally protective of the other eye. I don't consider crusting a definitive test for what is bacterial. The tear film has some antibacterial qualities & many random cases of conjunctivitis will self heal as they did before antibiotics were available. Your eyes should be fine