Finding out a spouse is having an affair is bad enough, but finding out others knew about it and said nothing is horrible. It causes you to not only harbor I’ll feelings towards the spouse, the AP but also to those who knew and said nothing. It makes you feel as if they condoned the affair.
Tell your dad. Be there for him and let him know you found out but don’t say you have known since Christmas. Just tell him you saw the text as if you just discovered them.
Edit.. Do not tell your mom because she will go into salvage mode and do everything to dismiss your story.
What do you think is going to happen when your dad finds out, and then finds out you have known since Christmas and didn’t tell him? You are in danger of destroying your relationship with your father. If you were a teenager I could understand it a little more. But you’re not.
You aren’t the one destroying the family your mother is.
Doesn’t your father have a right to the truth?