What do I do??

Okay I need mad advice right now. So I have this friend whom I've been friends with for almost 6 years now. He decided to come clean about how he's felt about me back in August and I was so surprised. He's very handsome, respectful and all around perfect. One big problem though. He used to date one of my best friends back when we were 16 (we're 21 now). They were always on and off after that but nothing really official. He decided to end things with her for good like 2 years ago. I really like him and the way he makes me feel. I don't really think we'll be jumping straight into a relationship soon, but I know we are going to get there eventually. I don't want to move what's going on between him and I yet because it makes me feel a bit uneasy because I'm not telling her. I have no idea how she is going to react and I'm kinda worried. My other friends tell me that it's going to be okay and that I'm doing nothing wrong but what do you all think? Should I stop this?