Making love with my cousin n my dreams
im 19yrs old. I live with my cousin (girl cousin) who is a year younger than me. I look at her as a close friend (almost a younger sister). We always spend time together whenever we have a time (eating dinner together, telling jokes, tickling each other, hugging, and other things that siblings often do). But i noticed that whenever we spend time together, i always (well, not always but most of the time) tend to have a dream of her making love/having sex with me. I dont know why im having a dream like this. Maybe it's just a sister complex or something. I don't really know.
My question is:
Is it normal? Am i the only one having this kind of dream? What makes me dream like this?
Added info's:
I find her attractive. I also have a girlfriend for 4yrs now and we are sexually active. And i have 2 half-sisters. One is 20yrs older than me and the other one is 16yrs younger than me.(just in case these infos are needed.)