Unfortunately feelings do not just go away and blocking someone today is easily undone tomorrow. Why is the AP treated with more scorn than your partner that betrayed you? Have you been given the full picture of the affair? Given what you have and there existing history, friendship, and work between them I find it doubtful this will not be a continuous problem moving forward with the relationship, I would suggest giving yourself some distance and time if you can as well as individual counseling. You are taking blame for being the cause but that is not true and neither is alcohol an excuse, in vito veritas, the idea of or the actual affair was already alive long before any alcohol was in the system that night. And now your partner is probably already looking at your relationship as irrevocably damaged, which it might be, and could be even more likely to cheat again if her insecurities triggered the cheating to begin with. If you want to make it work you will probably have to do couples counseling because you know what is more uncomfortable and awkward? Loving someone that you can't trust to not hurt you.