Hey I just looking for Some advice on an issue I've been with my fiance 7 years we have a child…

Hey I just looking for Some advice on an issue I've been with my fiance 7 years we have a child together I just recently went through an old phone he use to have and found out he did coke with my brother back in November now I haven't said anything yet I dont want to ruin the holidays for our son I'm just lost and looking for Some input