DEAR HARRIETTE: My friend "Mary" threw a small and intimate event over the weekend, and I ended up running into my ex-boyfriend there. He was there with his date, who just happens to be close friends with Mary. I felt blindsided.I wish Mary had warned me that he might be there, or that he is now dating a friend of hers. She must have known who was coming, as she asked all guests to RSVP for the ev…