Should I tell my boyfriend about my past?

You have know him for a year, and were best friends before he was you boyfriend. If you love him and he is still your best friend, you should be 100% honest with him and not feel like you have to hide anything. I hope once you do tell him it is a relief for you and then he can be your support. It sounds like you have a good relationship with him, so I don't think you need to have a third person there. A one on one personal conversation with him may be the way to go.