What should I do if my girlfriend of six years kisses another girl?

**For some background**, I met her in middle school, and we began dating back then. Our relationship ended toward the end of her senior year, but about a year ago, we rekindled our romance and became stronger than ever. I initially moved into her family home, and we later lived together in our own place for about four months. However, she struggled to regain financial stability, which led her to return to her family, while I moved back in with mine so we could save money and take things slower. Just today, she revealed to me that she has been drinking more often recently, something she had kept hidden from me due to her past struggles with substances. She mentioned an incident at work where she was "a little tipsy" with a female coworker in a private area. This coworker made a move and kissed her, and she admitted that she didn’t pull away. After the kiss, she claimed she needed to go back to work and hasn’t seen the coworker since. She only disclosed this information after I pressed her about another situation she mentioned that didn't add up, and it all came out. She started crying and expressed thoughts like, "You don't deserve this," and "I hate cheaters. I'm such a jerk for doing this to you." Now, I'm left feeling unsure about how to move forward. Our relationship is deeply intertwined; she’s essentially my childhood friend, and we’ve endured a lot of trauma together, which has strengthened our bond. My feelings for her are profound, shaped by years of knowing her intimately from ages 12 to 20. However, I've also had multiple conversations with her about the dangers of losing herself to substances. I've made it clear that I’m not sure I can stay in a relationship with someone who struggles with that and urged her to communicate anything she’s going through so we can work through it together. This is the third time she’s fallen into this situation, and I’m left wondering what could happen next and how best to handle everything.