Being Left Out

My dad left my mom for her best friend about six years ago and married her. I didn’t talk to my dad for about two years because of it, but I came to terms with wanting to have a relationship with my dad. I now put forth effort to be a part of his life as well as his wife’s. The problem… he treats her kids better than he’s ever treated me and continues to do so. I moved out and paid my own bills at 20 years old, yet meanwhile all three of her kids are in their 20s and still live with them/have all bills paid by them. My step mother doesn’t work and everything is completely paid for by my dad. My dad has a really good job making over 300k a year, and he spoils those kids so much. I now have a husband and a child, and he will buy my son the occasional gift but only if they’re getting gifts as well. On top of that, he took all of them to Disney World and didn’t even ask if we wanted to go. Now, he’s taking them to Aruba for a week and didn’t ask us to go yet again. Worst part is that we would happily pay our own way just to get the opportunity to spend time on vacation with my dad. Am I being crazy/spoiled? He never took me on vacations whatsoever when I was a kid and now these kids just get the perfect, fun dad I always wanted. It’s not even the vacations or the close that piss me off alone. He’s paid for all of their college tuitions, and meanwhile I’m still paying my student loans. On top of that, my step siblings have their own dad, although he doesn’t make near as much money. I just don’t know if I’m being a spoiled brat or not.