Hi Kevin, welcome to the forum. I hope you can find some information and encouragement here that will help you. I know what you mean about splitting time between your parents... my parents are divorced too--they have been since I was 2 years old--so I've spent my whole life dividing up birthdays, holidays, and other events between my mom and dad. And sometimes it is hard--people tend to forget that I'm only one person and I can't be in multiple places at once.
But at least you know you're not alone in how you feel.
Happy Birthday, by the way!