millstone around (one's) neck
A heavy burden. I wish I hadn't bought that house—the mortgage is a millstone around my neck.
a millstone around/round somebody’s ˈneck
something which limits your freedom or makes you worry: My debts are a millstone round my neck.A millstone is a very large heavy flat stone used to crush grain to make flour. This phrase refers to an old form of punishing people by tying a heavy stone around their necks and dropping them into deep water to drown.