Who should pay for the vacation?

So I have a boyfriend who makes twice my salary.  When we go on "family" vacations, meaning me and his two children, he has me pay for half of everything.  Half the rental car, half the gas,etc, and the trips we've been too have been to visit his family out of state.  We went to see his mother in Iowa and we also flew to MOntana to see his brother (without his two kids).  He would have gone if I hadn't. 

So he is taking his two kids to Disney this weekend and they are staying in the Value Resort.  After he booked it, he mentioned his daughters want to stay in the expensive Polynesian hotel next time and said I should go along too and pay for half.  And this just irked me to no end.  I've been to Disney with him and his children and it was not fun to say the least.  They are teenagers and they would literally bounce back and forth from Splash Mountain to Space Mountain, Splash Mountain to Space Mountain, over and over again waiting in the hour lines and wanting me to wait with them and I did and I rode it with them even though I have a heart condition but they pitched a fit when I wanted to stand in a 3 minute line to meet the Queen of Hearts.   

So I said, "No thank you.  I've been to Disney with you and your kids before and it was a miserable experience." To which he replied I needed to get over that and then I said,"Well, You make twice as much money as me and yet you want me to pay for half of a vacation for four people."  (and may I add that it was I who purchased his one daughter's annual pass and that I have an annual pass).  

Am I totally off on this?  Not that I am ever going to Disney World again with them cause I am not but I don't think its right that he has me pay for half on his family trips that  he has to go regardlessly.  He has to rent a car if I go or not.  He has to pay for gas if I go or not and yet he wants me to pay for half and then brags that he "took me" to Iowa or Montana.  I always say, "No you didn't.  I paid for myself."