Should I ruin my sisters marriage?
Why would you want to ruin her marriage?
Because she ruined mine first.
You shouldn't ruin other peoples' marriages. An eye for an eye makes the world blind.
Whatever.
If your sister was able to ruin your marriage, something else must have been going on, you can't place all the blame on your sister. While what she did was definitely wrong, you need to be the bigger person and not react in the same way she did.