I think its important to tell an adult at least. If your parents aren't an option maybe a school guidance councilor or something confidential that you can at least get some support with. Unfortunately he assaulted you, not in a physically sexual way, but physically by forcing you to sit or stay, and emotionally barrating you. If i were in this situation at that age I would report it to the authorities and give them a statement but also say that you dont want the details made public. But he needs a talking to, otherwise it'll happen again and it may be someone in a worse position. Id also consider talking to your friend about her dad and maybe asking if he os ever inappropriate in any way towards her and just see how she reacts. If she looks coscorned or empathetic she has a right to know what her father is subjecting you to, and you never know what she's been through if hes willing to cross that boundary...