While planning a vacation for two , this woman had no idea her friend would suddenly expect her to foot the bill. That's not how travelling with friends works — everyone has to pay their own share, unless you plan on a different way to split the costs that everyone can agree on. Even many couples will divide the cost of travel among the two of them to ensure both people pitch in. After all, travel isn't cheap, once the costs of hotels, flights, car rentals, food, and more, are all added togethe…