<human>: Can you summarize the given text in a few sentences?

Last Friday (6th June for late readers) I went to a pub where my friend was hosting his 18th birthday. Only at arrival did I know that my ex would be there as well. 

Just a little back story, after almost 3 years of being together we broke up since we had a very unhealthy relationship. Basically she was cheating on me for a good couple of weeks if not months while we were still together with her guy best friend. She didn't tell me and wasn't planning to ever tell me, yet she told quite a few people I know apart from me. I had to get them to tell me that she was unfaithful (she confirmed it and then blamed my friends saying they ruined whatever she had left of a friendship between the two of us). At one point she disappeared after i spent the day with her. She claims she went to "an abandoned sugar mill and had fun smashing the place up" with her friends from sixth form. I knew she was a terrible liar but that just takes the cake. I was furious with her and her mother called me asking me if i knew where she was, at the time I thought she was home already. She had me worrying sick. She eventually owned up that she was actually round her guy best friend's house (her current bf) after I confirmed with her sixth form friends that they took no part in smashing anything up that night, nor were they with her.

So I'm sipping on my cocktail with my 3 friends at the pub, well away from my ex when another friend who was next to my her comes over and tells me she's getting her bf (guy she was cheating on me with) to pick her up because I was 15m (≈45ft) away from her... I didn't even say a word to her and she left looking obviously upset/annoyed.

Did I ruin her fun at the pub with my sheer presence? Not that I care about that and I have no idea what goes through the mind of such a woman however it leaves me a bit curious as to what I should do in any unlikely future encounters.
<bot>: Broke up with gf after almost 3 years. Went pub, she was there coincidentally. She left after 15 minutes because I was there.