How should I view this?

Hi there! Even after three years, I'm still uncertain about how to feel regarding something my girlfriend did. I'm a 23-year-old male, and she is 20. Here's the background: When we had been dating for four months—she was 17 and I was 19—she attended a birthday party with her close female friends. Near the end of the party, they decided to play a game where they kissed each other. Although my girlfriend initially declined to participate, she eventually gave in due to her friends' persistence and the alcohol she had consumed. She ended up kissing one of her friends, whom I’ll refer to as "X" (she's female, and I should note that my girlfriend is heterosexual). The kiss lasted only a couple of seconds, was not passionate, and immediately afterward, my girlfriend felt awful, burst into tears, and reached out to tell me everything through chat. I reacted very poorly at first because, even though it was just a game, I viewed it as infidelity. I felt angry and sought explanations, especially since "X" often joked about finding my girlfriend attractive. My girlfriend defended herself by claiming she was drunk and succumbed to the pressure from her friends. Over time, I managed to move past it, and we gradually rebuilt our trust. She has since reduced her contact with those friends, and we've been together for three and a half years. Our relationship is now quite strong and stable. Still, I occasionally reflect on that incident, as it deeply affected me, and I never fully processed it at the time. I often question whether forgiving her was the right choice or if her reasons were merely excuses. The fact that I still feel unsettled by her occasional communication with those friends—especially since they insisted on the kiss despite knowing she was in a relationship—proves that I haven't completely reconciled this in my mind. Could this have simply been a matter of inexperience? (We’re each other's first serious relationship.) Was it justified for me to forgive her? How can I express my lingering discomfort about her staying in contact with those friends, especially since we haven't revisited this topic in three years?