Most of the time when I bring a new plant home it goes through a period where it drops leaves from the shock of a new environment. With Antheriums, If I'm not mistaken, they need pretty high humidity. I don't know where you live but a lot of plants do not thrive with indoor heating during the winter. You said you moved it outside so it sounds like you live in a warm area. I would not repot in the winter, wait until the spring. You probably will not see flowers again anyway until next spring. I hope your plant perks up!