Birthday Dinner - Who Pays and What Would You Have Done?

So it is my friend's birthday and she emailed her good friends inviting them to celebrate the day at a nice restaurant in town. She also said she had decided to reserve a private dining room and needed a head count. Dinner night we were escorted to the dining area. The waitress informed us that we were being treated to the chef's special tasting menu. During dinner six appetizers, five delicious entrees (including short ribs and "kobe" beef) and six dessert tastings were served. Everything was fantastic and I thought wow what a nice birthday party. Like all the guests I had also brought the b-day girl a nice gift. Finally the check came and her boyfriend took it an announced "OK the total is ___(several hundred dollars). We were to split the cost. Never when she was sharing these plans did she say "and you will be paying for it." I didn't make the plans, she did! I handed the guy $40 which was below my share but what I would have spent on a dinner there. What do you think?