<human>: Could you distill the essence of the text into 1-3 sentences?

My bf(21) and I(20) have been together for a year and a half. We just got back from 4 great months of traveling together. We've been back for about a week now and I went out for coffee with my best friend last night, we'll call her Kathy. 

It turns out that she got really drunk and cheated on her bf of 4 and a half years(they're both 21). In my previous relationship that lasted for 5 years I had cheated on that boyfriend twice; so, when I got together with my current bf he knew about my background and we have a mutual agreement that if we did cheat on each other we would say something. Kathy said that her bf had said to her if Kathy cheated on him he wouldn't want to know and if she did he would break up with her. I didn't really know what to say so I didn't say much. 

This morning when I went to my bf's and told him what happened he immediately told me to text Kathy and say that she had to tell her bf that she cheated on him and if she didn't then he would do it for her. My bf said because I didn't tell her that in the first place it didn't reflect very good on us. 

So now he's pissed off at me and said that I won't hear from him for the next couple of days, maybe a week. He said that I need to choose between my boyfriend and my best friend and that maybe I need the week to learn who I really am and what good comes from telling the truth.

Did I really do something wrong? Does he have the right to be mad at me? Is it right that I choose between my boyfriend and my best friend?
<bot>: BFF cheated on her bf, I have a background of cheating and my current bf(that I've never cheated on) is mad because I didn't tell my bff to come clean to her bf.