I love my cousin but...?

Okay so i have a little cousin. Shes 10. Shes cool i guess but it just really annoys me that she comes over every freakin day! she lives upstairs so she comes whenever she wants and leaves whenever she wants. I had problems with my boyfriend coz he came over everyday so now he comes over like 3 times a week..wich is perfect! the reason i wanted him to leave was bc i wanted time for myself and do my stuff, but it defeats the purpose if my cousins gonna be here! & when my boyfriend does come over, i appreciate it now and sometimes i just wana be alone with him, not to do nasty stuff, just to be with him, but shes always here. Im a really nice person so i cant just tell her go away or something coz ill feel bad. it took me months to tell my bf i needed space. idk why, its jus how i am. So what should i do about this??