Ideally store leftover sauce portions separately from pasta. Leftover sauce can stay in the refrigerator for several days. I haven't noticed any issues with the texture separating or otherwise getting weird. Gently reheat it, stirring in a splash of hot pasta water to thin it out if it thickens up too much in the fridge. Leftover pasta portions coated in sauce can just be reheated in your preferred manner, with a little extra splash of milk to bring back some of the creaminess.