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

Me: Male 21
Partner: Female 20
Relationship: 2 years

So, my girlfriend and I attended a party with mutual friends where we both became incredibly intoxicated, nothing unusual. My girlfriend is fairly close to one of our mutual friends and they hooked up (I could hear them making a ruckus). I told them I knew they were in there and waited for them to leave, they both apologized and we hugged it out. I don't want to know what happened, nor do I care. My girlfriend took my aside and told me that she regretted it (not just because of me but because she never saw the mutual friend in that way and she doesn't want to ruin the friendship). She said she would understand if i decided to break up with her but I don't want that, I love her, she loves me and we have never had a dishonest moment in our relationship, we have always both been able to genuinely convey our feelings and concerns to each other. I know everyone makes mistakes and we are all prone to weakness at some point, I believe forgiveness is key to a positive life.  So despite not being mad or upset about it (in fact we are even happier than we have been prior to the incident) a few of my friends are giving me a tough time about this and are trying to convince me to dump her out of principle, so Reddit, did I make a mistake here? We are both happy so why should 'principle' matter?
<bot>: Girlfriend cheated and i'm not worried about it, but other people are making are judging me negatively and telling me to dump her out of principle.