My friends boyfriend and friends ex keeps flirting with me.,,what should I do?

I'm in sixth form and will be 17 next month. I have never been kissed and am extremely shy. Just had cancer but no chemo etc only surgery as I was very lucky. I have lots of scars and skin grafts on my hand because of this which I am too afraid to show. Anyway, one of my best friends - ellie went out with a guy called Dale and she was very confrontational and only dated for a month but she was gutted. He is now going out with my close friend Becky who is like me (quite shy) and she liked Dale for a long time. However, he does have a reputation but he had started to flirt with me o social networking sites which Becky or Ellie don't have. I knew him before he came to my sixth form and he has been flirting with me since I said hi to him one day. I know he is a typical flirt and it probably means nothing but what do I do? I haven't been flirting back but I have been replying to him. However, I LOVE the attention he gives me as I don't get any and I haven't even had my first kiss. Should I tell him to back off or do what I want to do for a change and live my life for once? What should I do? If I flirt ellie will kill me as 'no exes allowed' but she has also been with LOADS of guys. Shall get some excitement?