You are going to learn that people don't hold others in the same regard as you do, nor do they stand by the wounded party.
You can not make anyone do anything or NOT do anything. We none of us have the slightest control over another living being. Your husband betrayed you, he knew what he was doing and did it anyway.
Sure these people are not great, but you will sadly see that your friends will stay in touch with whoever they like. Hopefuly staying in touch with you but also with them. they wont want the drama, although at the same time will pick over the gossip for sure.
With regard to your wider friends group, you sending this letter could even have harmed your chances at coming out 'on top', they will think you are crazy, and that as a couple you and the cheat are somehow a bit of a mess, and something they don't want in their circle.
You have no control over any of this. I get why you would want to have them tarred and feathered and pilloried in front of the world, but that is often the opposite of the way things go.
How are things with H now? is he working on regaining your trust? are you in counselling? do you have kids etc? how long have you been together?
Is looking over your shoulder the way you really want to spend the rest of your life?