Jennie Garth and Luke Perry stood together for "Beverly Hills, 90210" in front of the camera. Now the actress talks openly for the first time about how deep her feelings really went – and what this experience is doing to her to this day. It's a story that remained unspoken for a long time: Jennie Garth, 54, talks openly for the first time about what Luke Perry, †52, really was for her. "The truth is, he was my first great love," she writes in he…