<human>: Can you condense the text into a few key points?

So there's a nice little golf resort just under 100 miles from the city where I (18m) live. I went there this past weekend with some of my cousins who were visiting from out of state and that's where it all happened.

We had just done 2 rounds when we headed to the bar and to my greatest shock, there was Mr Smith (45m) {not real name} with another woman who clearly was not Mrs Smith. They were having wine and Mr Smith was constantly touching her face and hair. Our eyes met and we waved at each other but I could tell he had become very uncomfortable and they left no more than 5 minutes after.

Fast forward to yesterday, me, my dad(46m), Mr Smith and Jamie(Mr Smith's son & my best friend) all went to play tennis together as we normally do every other week. It was here that he asked me if I had told Jamie about what I saw and I told him no, I hadn't. He then asked me to keep it a secret and slipped what turned out to be $600 into my hands and said "lets let it stay between me and you then" and then asked me if we had an understanding, to which I just nodded.

I've been friends with Jamie(18m) since kindergarten and our families are pretty tight. I honestly just don't know what to do. I haven't told anyone besides my two cousins but I feel incredibly guilty and anxious about this whole thing. If I don't tell Jamie, and he somehow finds out that I knew and accepted bribe money I believe it'll be the end of our friendship. I've thought about telling him but I honestly can't even bring myself to starting a conversation like that. What if I do tell him and his family breaks up because of it? Or worse, what if I tell him and he doesn't believe me? Either way I just hate that I'm even in this situation. I resent Jamie's father also for putting me in it. What should I do?
<bot>: Best friend's dad offered me money to keep his affair secret. Should I tell any way or keep out of it?