I am in the same boat as you. Quite a few people ended up knowing.
And I am positive it got around because I have NEVER been asked what OW/xBFF is up to.
I think my Mom was a big source of starting the gossip going. I don't think she had those intentions, but with OW/xBFF and her parents being such a big part in all of our lives, there was really no way to avoid it.
And to be honest, I do not care at all that people know. What they see now is a family that has worked through it and stuck together even though it has been hard.
And if for some reason someone looks at us (me) as weak for staying, well all I can say is I am happy they have never been through it. People are ignorant about things they do not understand. And I hope they never have to understand.
So, as far as being proactive and telling more people, I would think you don't really need to. If it comes up in conversation, say what you want or don't want.