Caught My Sister's BF Cheating

I stumbled upon something I never wanted to see—my sister's boyfriend with another girl. My heart dropped. Do I break her heart with the truth, or do I hope she finds out another way? I feel stuck between protecting her and the fear of being the bearer of bad news. It's a weight I'd never wish on anyone. How would you handle this? Does loyalty mean exposing the truth? #FamilyDrama #ToughChoices #TruthHurts