Moving to Spain, How hard is it?

I am 18 in a month and me and my boyfriend have been together for 3 years now. He moved to spain 6 months ago when he turned 22 to be near his dad who is spanish and once i am 18 i wish to move out there with him . I have been taking spanish lessons for the past two-three years as i have known i will live out there. Anyway what i want to know is how i would go about moving there ? i live at home with my parents and have just finished my a-levels. I would be living with my boyfriend so i wouldn't need to worry about finding a house etc. if it helps we will probably get married in the next year or two also.. I would really apriciate any advice you could give about how i would go about moving :) oh and i have a british passport always have and i'm a british citizen. Thanks x