What should i do both my best friends are cheating on their partners with each other.

Recently my bestfriend (F), & my other bestfriend (M) have been getting really close with eachother. They are both in long term relationships with their partners. I grew suspicions because i would drink with them both & they’d say they were going home & i would get dropped off first. i have both their locations & i usually check their locations to see if they got home safe. Id seen that my friend (M) would stay out with her for about 2 hours. 2 days ago we had drinks again & i decided that i wanted to see if they’d do anything alone (sexually). I left my burner phone in the backseat hidden, making sure to atleast catch some audio. a couple days (today) i was able to retrieve my phone & even though the audio was muffled i was able to makeout the noises of yk… i feel truly confused on what to do & don’t want to ruin my friendships especially since they both have partners but i would also want to be told if it’s happening to me. please help!!