my boyfriends daughter

my boyfriend and have been together 13 yrs. his daughter will be 21 next week.she dose not live with us,but stays at his brother and sister in laws home for 4 to 5 yrs. he pays her rent and also gives her an allowance.on top of it for all these yrs. my b-day is two days after hers,and my boyfriends x's b day is the same day as his daughters.she always seems to be invited to the daughters party and all the family not only flocks her the'er there with presants and such.nothing for me not even an acnoligment.I want my boyfriend to stop paying anything for his daughter as far as living {rent}.she's done with college and my boyfriend owes child support up the ass.am i wrong for wanting him to stop paying this girls rent and allwoance?should i say something to his family?should i leave?HELP!!!