It’s an exclusive club no one wants to be a member of. That’s how several people explained why they were at a “Grief, Sweat, & Tears” event this spring, at which about 25 men and women met up for a double-header barre and spin class. When everyone gathered in the lobby to chat afterward, sweaty and smiling, conversation flowed as naturally as it would at a bar — but death and grief were the main topics, with people trading stories about lost loved ones. “It’s obviously something that people are not naturally inclined to discuss,” Margot Lichtenthal, a past Grief,…