What should I do about the girl I like?

I met this girl about 3yrs ago and I started to like her. I started talking to her alot, and thought I had a chance. When I asked her to be my girlfriend six months later, she said no. A couple weeks later, she started seeing her ex boyfriend again. I started thinking I was too shy. The next year came along, and I started talking to her again. I was no longer shy, and those feelings came back stronger. It is now in the present, and those feelings are still there. Whenever I talk to her, it becomes the highlight of my day. I cant imagine liking another girl, and other girls are not as attractive, because she is not her. The only problem is she is still seeing her ex boyfriend. We still talk, and sometimes she talks abut her boyfriend, which is hard for me to hear. I want to tell her that I have strong feelings for her, but I dont want to lose her out of my life. She is too important to me for her to leave my life. So do you guys think I should tell her, or not tell her. If you think I should tell her, how could I tell her without making our friendship awkward. If I shouldnt tell her, what should I do? Thank you