<human>: I'm just looking for some input to see if you all think that I should say something, or if I should just not get involved. 

My good friend, let's call her Nancy, has been dating her boyfriend, Tom, for just under a year and a half. From Day 1 when they met she was cheating on him both emotionally and physically with another guy [M25] for about the first 9 months of their relationship. She decided that she no longer wanted to see the other guy because she could see it was going nowhere, so they ended their "relationship"; all the while continuing her relationship with Tom. 

My husband and I [M27,F26 respectively] were out at a club one evening recently when we saw Tom making out with another girl. Tom knows that my hubby saw him, but has no idea that I also saw. 

The question I have for everyone now is: should I tell Nancy about this, or just let it be since they could consider this "even" since she cheated on him, and he cheated on her?

Can you provide a brief rundown of the text in within 3 sentences?
<bot>: I saw my good friend's boyfriend making out with another girl and am unsure if I should tell her. I'm torn because she was cheating on him at the beginning of their relationship for just over 9 months.