My partner was unfaithful to me five months ago. I'm [M:23] and they are [M:30].

Hello everyone, I don't usually turn to Reddit for advice, but this is something I feel uncomfortable discussing with people in my personal life. I'm a gay man in a relationship with my partner since September 2021. Over these three years, we've faced many challenges and tough times together. My partner is a recovering alcoholic and has been sober for about four months. I have to say that things have been going really well lately; he has completely transformed his old habits and is actively addressing his mental health. However, there was a period of about nine months to a year when alcohol misuse led to many arguments between us, almost pushing us to the point of separation. About five months ago, after a major argument about his binge drinking, he confessed that he had hooked up with someone else during a blackout as a misguided way to "get back at me." I only discovered this after finding an old STD test, which raised my suspicions since we've always been clean. He expresses deep shame and regret, insisting he would never have acted this way when sober, but that doesn't change what happened. I can't fully articulate the anger, sadness, and sense of betrayal I'm feeling right now. I'm reaching out to you all with a question: What should I do next? I know ultimately, the decision is mine, but I'm hoping someone who has gone through a similar experience might offer some insight. Thank you all for your support.