Should I be supporting my girlfriend and her son on vacation for a fair amount of money?

My Girlfriend was in a bad divorce. After her marriage she moved in with me along with her now 13 year old son. I pay all the expenses for the house except for Groceries. Her only bills are a car payment of 300 a month and cell phone bill. I cover her health and car Insurance. She get's 2,000 a month from her ex and I give her 2,500 a month also so she doesn't need to work, She takes care of the home, Her Son and buys groceries. We have been dating for 5 years. during this time I have paid for all vacations, Dining out, trips for her and son to go away to visit her oldest son.

We have enjoyed very nice vacations, she wants to take her son and a friend of his with us for a 4 day vacation, the vacation is one they went on before but didn't stay in a nice place and had a really bad time. She wants her son to see what a really nice vacation is like, She wants me to foot the bill for 4 of us, Myself, Her, her son and son's Friend. I wouldn't take my own kids on this type of trip and I don't feel it's right that I pay for her son and his friend. I think she should pay for the two of them with the allowance she gets each month from her ex. Were talking about 1,800. She flipped out on me, that I don't like her son, that she doesn't have any money and I'm trying to control her. Saying I will only pay for trips that I approve and not treating her son well. by the way I drop her son off at School each morning and we get along great. I just don't want to set a precedent of her planning trips and me paying for things I don't want too.

Should I be supporting my girlfriend and her son on vacation for a fair amount of money?
Post Opinion