Cook the fettuccine pasta according to package instructions.
Drain and set aside.
In a large skillet, melt 2 tablespoons of butter over medium heat.
Sauté the garlic until fragrant.
Add the shrimp, scallops, and mussels to the skillet.
Cook until the shrimp turns pink and the mussels open.
Remove the seafood and set aside.
In the same skillet, add the remaining butter and heavy cream.
Bring to a gentle simmer, then gradually stir in the Parmesan cheese until smooth.
Toss the cooked pasta with the Alfredo sauce and seafood.
Season with salt and pepper to taste.