I wasn't truthful at the start of my relationship, and now it seems like it might come back to haunt me.

I’m a 26-year-old male, and my girlfriend is 28. We’ve been together for six months now, and I’m utterly happy with her; I truly adore her. It didn’t take long for me to realize she might be “the one.” However, I made a significant mistake at the start of our relationship. Before we met, I had plans to attend an outdoor camping event with a female friend who had previously expressed feelings for me, which I had firmly declined as I didn’t feel the same way. We remained acquaintances, and I offered to drive her to the event since she didn’t have reliable transportation. I was clear about needing her to bring her own tent and that we wouldn’t be spending the entire time together; I was simply providing a ride and some guidance. And that’s how it played out—nothing more happened between us. In the weeks leading up to the trip, I met my girlfriend, and we made things official about a week before the event. I decided to tell her I would be going alone and didn’t mention my friend. At the time, I rationalized not telling her because I didn’t want to abandon my friend, and I feared that mentioning it might make my girlfriend jealous and break trust. I convinced myself that since I would be effectively alone, carpooling wouldn’t be an issue. I also didn’t inform my friend about my new relationship for reasons I still can’t fully understand. The trip occurred without incident, and about three weeks later, I told my friend about my girlfriend. She was happy for me, but she still believes we became official after the camping trip. Now, six months later, it’s time to make plans for this year’s event. I’ve told my girlfriend how much I enjoy it and invited her to come along. Unfortunately, my friend has also planned to attend and has already bought tickets. She even asked for the contact information for the campsite we used last year. I’ve secured our camping arrangements, and if I back out now, I might lose that spot. However, I’m more concerned about the possibility of my friend and girlfriend crossing paths and the risk of my girlfriend discovering that I wasn’t alone last year. The thought of hurting my girlfriend is unbearable. She’s one of the kindest and most wonderful people I’ve ever known, and the idea of causing her pain is gut-wrenching. I realize now how badly I’ve messed up and how misguided my justifications were. I should have been honest and upfront from the beginning. I’ve been transparent about everything else, but this secret is weighing heavily on me with shame and guilt. If you’ve read this far, I’m seeking advice. I fully acknowledge how wrong I’ve been, so where do I go from here? Should I come clean? Do I skip the event this year, even though I’ve expressed how much I enjoy it? Should I talk to my friend about this situation? Or is there something else I should consider?