I just posted something on the general forum and thought you may find it useful, so have reworked it to be applicable to your scenario.
Firstly I'm sorry you're going through this. This is an incredibly painful and disorienting situation, and it's completely understandable that you're seeking clarity. There's no single, universally "correct" answer to "what do I do now?" after infidelity, as the optimal choice is profoundly individual. The path you take will be intrinsically linked to your own core character traits.
To begin, I encourage you to reflect deeply on your own temperament. Consider if you align more with these traits:
High self-belief: Do you hold a strong conviction that you deserve better than a situation involving betrayal?
Unmovable principles: Do you have a firm moral stance against infidelity that you feel cannot be compromised?
Highly logical nature: Do you tend to prioritize rational considerations over purely emotional ones in major life decisions?
If you resonate strongly with these characteristics, then happily reconciling might prove impossible for you. A high self-belief would likely prevent you from accepting a diminished perception of your worth by remaining with a betrayer. Your unmovable principles would likely preclude staying in a relationship that fundamentally violates your core values. Furthermore, a highly logical approach might lead you to view the "intangible" aspects of reconciliation as less significant than the practical reality of the betrayal, recognizing the vast pool of compatible partners that exist. For individuals with this outlook, divorce often offers the most direct and assured route to recovery.
Conversely, you might find yourself aligning with a different set of traits:
High empathy: Do you have a strong capacity to understand and share the feelings of another, including your partner's potential remorse or struggles, and a desire to explore the root causes of the betrayal?
Regard for forgiveness as a high virtue: Do you believe forgiveness is a moral imperative and a powerful path to healing and rebuilding?
Highly Emotional Nature: Do you tend to prioritize the deep emotional investment, shared history, and unique bond built over time, even above purely rational assessments?
If these traits resonate more strongly, you might be inclined to pursue reconciliation. Your empathy could allow you to understand his struggles, and your value for forgiveness could drive you to seek healing and rebuilding. Prioritizing emotional connections and shared history might lead you to preserve the relationship despite the betrayal. As the text notes, reconciliation is often more prevalent among those who highly value forgiveness, including religious individuals, and there's a correlation with higher empathy.
Given that you are 30, without children, and the affair was relatively recent and involved "drunken kisses" but also "daily messaging" and continued communication even after the other partner found out, these specifics are important. Your partner's claims that it "meant nothing" and was "just a distraction" are also part of the emotional landscape you must evaluate through the lens of your own core traits.
Ultimately, "do you need to leave?" is a question only you can answer, based on this deep self-reflection. If you choose to leave it could be the "fastest and most assured route to recovery." If you choose to attempt reconciliation, be aware that it is a profoundly challenging path requiring immense effort from both sides to rebuild trust and address the underlying issues. Regardless of your decision, prioritizing your own healing and well-being is paramount.