Dear Amy: I became friends with a co-worker, “Marilee,” two years ago. We developed a great friendship. I recently invited another girl, “Trina,” into our friend group. Trina does not work with us, but we have other common interests. Recently, though, Marilee and Trina seem to have bonded and are gradually excluding me from things — tubing, brunches, beach trips, etc. I am feeling left out and hurt by this.