Any advice?

It's hard for me to open up to anyone new. It's been a few months since I found out my ex cheated on me and my best guy friend of almost 6 years admitted he's always had feelings for me. He's the guy I tell everything to and I did start liking him the last week I was with my ex. I felt completely comfortable with him when we were friends but when he asked if we could be official, it's like it restarted everything and I'm all shy about certain things with him. I'm 17, I'm not new to dating but going from best friends to more than friends scared me because I would've never expected him to have feelings toward me. He's amazing in every way and I always thought he'd make a lucky girl happy one day. I want to be that girl now! But I don't know how to shake this feeling of being shy around him.