My best friend?s boyfriend cheated on her and my boyfriend knew the whole time

TL;DR: my best friend?s (21f) boyfriend (24m) cheated on her and my boyfriend (24m) knew the whole time and didn?t tell me (21f)
I (21F) have been with my boyfriend (24m) for over 2 years now and today I just found out that my best friend?s (Sara, 22f) boyfriend (Sam, 24m) cheated on her during the first 2 years of their relationship (total 3 years). It was over a year ago that my bf, my friend?s bf, and Sam all went out to the bars together where Sam apparently made out with another girl. My bf and my friend?s bf both saw him make out with the girl and decided not to tell anyone to honor ?bro code? because it ?wasn?t their business? to tell any of us girls, including Sara. I only found out because my friends bf confessed all he knew to me and my friend.
Apparently that is not the farthest Sam has gone with cheating on Sara (my bf did not know this part) as he told my friends bf that he has fully cheated on Sara multiple times with multiple different women throughout their entire relationship. I 100% plan on telling Sara as soon as she gets back from a trip. I don?t condone cheating of any kind and I know that she would want to know what Sam has been doing behind her back.
However, I can?t shake the feeling that my bf keeping this secret from me was wrong. He?s not very close with Sam and I feel disappointed that he took Sam?s side over doing what was right and telling either me or Sara herself what really happened.
Am I being dramatic for feeling disappointed in my boyfriend and like I lost some respect for him for keeping this secret for so long?


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