Set a pot of salted water to boil. Prepare the tortellini according to package directions.
Meanwhile, in a large skillet over medium heat, sauté the onions until translucent and fragrant, about 2 minutes. Add the garlic and red pepper flakes, cooking another 1 minute. Add the Italian sausage to the pan and cook until brown, breaking it up with a spatula as you go. Deglaze the pan with the white wine, allowing the wine to simmer for 1 minute. Pour in the diced tomatoes and tomato sauce. Stir together and bring the sauce to a simmer. Season with salt as needed to taste. Remove the pan from the heat and stir in the half and half and spinach, until the spinach is wilted and the cream is well incorporated into the sauce. Fold in the cooked tortellini. Serve in pasta bowls.