10 months ago I was out of the country for a period of three months for work reasons. During this time, my partner cheated on me with one of his friends, who is also one of his colleagues. This person is part of my partner's extended friendship/colleague network, i.e. the friend/colleague of a number of my partner's friends/colleagues. My partner has not told any of these friends/colleagues, even those who he is closer to, about his affair. My partner's ex-lover knows that I know about the affair.
I am often invited to events related to my partner's work, or to social gatherings including this network of friends/colleagues. I have previously enjoyed these events and know his group of friends/colleagues well, but since my partner's affair I feel very anxious that I will be unable to deal with the presence of my partner's ex-lover. This is not just due to my generally feeling uncomfortable around this person, but also because I am not sure how to act naturally in front of the group of my partner's friends/colleagues in this context.
Without running away from my partner's ex-lover all night, how do I handle this kind of event? Are there any techniques I can use to avoid/minimise interactions with my partner's ex-lover without making it obvious to his group of friends?
Edit: Cultural context: England (I am not English so can get away with being more direct), liberal, academic crowd