I'm so sorry this didn't work out as you had planned. I guess now is as good a time as any really... at least Christmas was over.
I wouldn't be too thrilled about anyone taking my phone out of my hands, sister or not. That sounds like it was a bit rude. Perhaps this is her way of being playful? (Mono just said I would fucking lose my mind... he's right
In light of that I think if it were me I would be inclined to tell her that while I acknowledge her concern, she did find out by snooping in my personal stuff and before she goes off about it she best educate herself before hand... then I'd give her some book ideas and links and tell her t get back to me.
When my husband and I came out to my parents they had similar concerns and took them to the extreme because of their belief that they had a right to think their concerns were reality. Be carful. I hope your sister is not the type to blow the whole thing up for you in regards to other relatives (even in a gossipy way). Not to mention just blow up in general.
What I don't get about your first post is, did she say she had affairs in front of her husband???!!! Just interested. That's how I read it.
Mono and I think that people have affairs because they think they will end at some point and that is all they want to invest in. They are trying NOT to hurt their partner in light of that thought/theory. Besides that they really don't want their happy little image of being a great and well put together family to end.