Girl flirts with me a lot, I act like I dont care, but I do, I get nowhere. Help. Please.?

I like this girl, she flirts with me times (holdin hands, sitting on lap, etc.), but she does a lil flirtin wit other boys too and she in a 'its complicated relationship' so I dont know what to do...on top of that, Ive never been in a relationship to know how to start one and dont know places to take her to but I want to to be with her. Anyways, Im not the only she flirts wit so I get frustrated sometimes and block the flirting. How can her like this? Thanks in advance. P.S. yea Im embared as hell, but thats how much I..u know...