Sticky situation with friend

Okay, well like 3 months ago I thought my life was over when me and the ex split up. I was a wreck for the first weeks until I started doing no contact. I finally started feeling better and started going out looking, for women again. Well I started hanging out with my friends and some girls and about a week ago I started seeing some girl. Well here is the sticky part: I kind of dated this girl like 5 1/2 years ago for like a month but at the time we were both really young (I was 17, she was 15). Nothing really came out of it. Well we went our separate ways and I actually became friends with the guy she started dating. Well last saturday she goes out with a few of her friends and my name comes up. Well apparently she has wanted to be with me for the past 5 years. I had no idea and the time was never right because I was involved and so was she. We started hanging out about a week ago and things have gone very smoothly. We are very compatible and we have had some good times so far. Here in lies the problem: My friend has no idea that we have been seeing each other. Don't know how to tell him and I know that a lot of people will be mad at me. Things happen for weird reasons and what has happened lately I don't feel like giving up on. Not sure what I should do. Really need some advice.

Erm This is a tuffy.. I don't know I would be straight up with her man? or friend whatever he is and if you lose your friend's over it so let them be like that. Don't let noones judgement or opinions make urs for you. :P