What would you do in my situation

My best friend K has a boyfriend called D and one of his friends told me that when they went to the strip club for their ‘boys weekend’ he was in a private room with a stripper doing god knows what . Immediately I told my best friend because I thought it was the right thing to do. She then texted him and all this shit started. I really like her boyfriend and didn’t want to start trouble those just were not my intentions but it started. As soon as there was drama I immediately regretted my actions and I really didn’t want to be the bad guy, but I thought as a duty to my best friend I should of told her. This all went down between 4 and 6:15 am this morning. I woke up with a text from her saying that D might slap me. What is this. I really tried to do the right thing now i have literally lost two friends and started conflict. This is so shit.  What would of you done in my situation if someone pretty much told you your best friends partner cheated on them?