Thoughts After a Slip-Up

I broke up with my girlfriend last week. We had been together for three years and everything was good, she’s caring, she understands me more than anyone else ever has. But we got into an argument over something trivial that spiraled out of control and I ended things abruptly, without really thinking it through. Now I’m alone, but still very much in love with her. I went to a friend’s party the other night while all this was fresh and I found myself drunk, chatting with someone who seemed interested. One thing led to another and... well, it’s not something I usually do, but I sort of... slipped up. It felt out-of-character for me at the time, almost mechanical, like my body knew what to do before my mind caught up. I’m confused about why this happened. Am I just looking for any kind of physical connection after being with someone so long? Or was there something in particular about that night or that person that made it feel right? The fact is, the experience has left me feeling worse, not better. It’s been days and I can’t stop thinking about my ex-girlfriend. Was this just an act of desperation to fill a void temporarily, or something else entirely? Does anyone know what might be going on in my head here?