I discovered my girlfriend discussing plans to leave me in some text messages.

I'm a 26-year-old guy, and my girlfriend is 25. We've been together for almost nine years, and like any relationship, we've had our ups and downs. Overall, I thought we were doing pretty well. We moved out of our parents' homes together at 17 or 18, and we both share a house along with our eight-year-old dog, who we raised together since he was a puppy. Every day after work, we take him for walks and visit parks. My girlfriend works from home in a job that involves computer work and meetings, although she sometimes has free time. She has a close friend from high school named Natalie, who lives five hours south, and occasionally, my girlfriend visits her and her two sisters for about a week at a time. Now, for the more complicated part. In July 2024, my girlfriend invited Natalie and her sisters over for a sleepover. They asked me to get them MDMA/molly, and I unwittingly agreed, thinking they just wanted to have some fun. However, they ended up spending four hours locked in the bathroom, giggling and whispering, while I sat downstairs feeling neglected and wanting to sleep. After trying to distract myself for too long, I finally lost my cool, banged on the door, and demanded to know what was going on. I accused them of being intimate in a jealous panic, and things escalated into a heated argument. After that night, my girlfriend and I struggled to rebuild trust. Months passed, and despite my attempts to work through it, she began threatening to break up with me over how I handled things that night. I've tried to adjust my schedule to align with hers so we can spend more time together, especially since the chilly weather makes early mornings challenging for me. Despite my efforts to prioritize her, she has grown increasingly distant over the last few months. Recently, I noticed her phone password had changed, which was unusual for us since we've typically shared that kind of information. When I discovered her new password, I snooped and found concerning text messages between her and Natalie. They were discussing potential rental applications and plans to leave me. This realization has left me feeling deceived and confused. Now, as Valentine's Day approaches, I'm conflicted about planning for it, knowing she seems to be plotting her exit. Friends around me suggest I let her go and focus on myself, but I feel like we've invested too much into our relationship to end it over one bad night. I worry about how our dog will react to such a big change. I'm seeking advice: Is this worth fighting for? Am I being irrational or unreasonable? Is she overreacting, influenced by her friend's opinions? What should I do in this situation? Any guidance would be appreciated before things escalate further. Thank you for your input.