Not happy with my broker's performance.

Read the agreement! And talk to the broker and/or their supervisor, presuming they aren't some sort of solo shop.

Just curious, what part of his performance are you unhappy with?

You can usually request termination for non-performance. Keep in mind that agents don't want to work with sellers that aren't happy with them - talk to the agent and ask him/her to release you. That agent will be entitled to a commission though if anyone saw it through them prior to the break of the contract.

I'm curious what made you choose that particular broker to begin with?

Usually there is an exclusivity period in the contract. When I sold my last apartment it was 60 days. After 60 days I could get another broker. Do you have something like that in your contract?

Even if you can't "cancel" it as such, in practical terms you would be able to prevent a sale from occurring by being unavailable for showings and open houses, upping your asking price, etc, if you so desired. Not recommending that you go down these routes, but if you were to hint at some of these possibilities, your broker would probably much prefer to just let you walk.

I shake my head whenever I hear stories like this. Why do people still sign traditional Exclusive Right to Sell Listing Agreements for 6%? Not only are you tied down potentially for 6 months, but if a "ready, willing and able" buyer is found at your listing price and you decide to back out, you STILL owe your listing broker 6%. Unreal.

Just remember, you can access the NYC MLS (i.e. RLS - REBNY Listing Service) without a traditional broker these days. Inman just broke the story: https://www.inman.com/2016/07/25/the-underground-for-sale-by-owner-movement-in-nyc/

>Not only are you tied down potentially for 6 months, but if a "ready, willing and able" buyer is found at your listing price and you decide to back out, you STILL owe your listing broker 6%. Unreal.

nonsense. This is an industry scare tactic.
Until you are at the closing table with a fully funded transaction and a buyer who has signed a contract, you do not know you have a ready, willing, and able buyer.
Furthermore, any brokerage even willing to attempt to collect a fee on such basis against an ordinary homeowner is short-term simple minded. What would the owner even pay you with - a lien against the property?
This is beyond ridiculous to assert.

consult an another attorney.

Before you do anything, read the agreement and see if it states something concerning termination.
Then explain your situation to the real estate broker. Depending on the situation, it may actually be beneficial for her/him to terminate the contract too.
If you fail to manage it, then seek agreement termination in the County Court. You should probably hire a lawyer then.