Cook macaroni according to package directions and then drain. In the meantime, in a large saute pan or pot melt the butter over medium heat and then stir in the flour and mix until sand like. Gradually whisk in the milk. Bring up to a boil, whisking constantly and then cook for 1-2 min. or until thickened. Add salt and pepper to taste. Stir in the cheese and stir with a wooden spoon until melted.
Pour in cooked macaroni and lobster, stir gently. Warm the lobster through and serve immediately.