Yikes. That doesn't sound like what a normal D/s relationship has. Dominants aren't supposed to make submissives feel sad. Safe to express sad feelings they already have? Sure. But inflicting sorrow and fear onto them? Please be careful. You can create a trauma bond if you're not careful. When the D/s relationship ends you want the subs to be in as good a mental place as they were when they started, if not better.