Cousin is over controlling

My 16 year old cousin who is like a sister to me always wants to be around me. I’m 17 turning 18 in January. I have a boyfriend but I rarely spend time with just him. She told him that he needs to tell her a day in advance whether or not he’s hanging out with me. Blew my mind when I found out she said that to him considering I don’t even tell my mom my plans a day in advance. My boyfriend cooked dinner for me so I went over to his house and she literally found any reason for me to stop what I was doing with him and to tend to her. This is a constant thing. She said she wants to hang out with me as much as possible before I go to college (keep in mind my college is going to be an hour and a half away from her) but that she understands that my boyfriend wants to hang out with me before he leaves for army bootcamp in July(which I don’t really think she cares at all) What should I do?

EDIT: me and her hang out like 4-5 of the 7 days of the week. So we hang out and spend a lot of time together. And if I want to spend time with my boyfriend she tries to guilt trip me and she throws a pity party about the whole situation and gets pissed off at me.