I am new to cryptocurrencies and Bitcoin specifically. I recently made a transaction by transferring some Bitcoin from my GDAX wallet to my Binance wallet.

Here is my public key: https://blockchain.info/address/1CQUN1tN1BrD8dPtqFjUeKRGcdYmEhdafh

Why is the sender of the Bitcoin from an address that does not belong to me? I checked my GDAX public key which changes every time I refresh the page.

If you click on the the public key that sent the Bitcoin, it shows that it has made another transaction for 0.98504441 BTC to a different address.

So I have a few questions:

1. Why does my Bitcoin public address change everytime I refresh the page on GDAX?
2. Why does the sender of my Bitcoin also have another transaction to a different public key?
3. Does GDAX send out Bitcoin from a shared wallet on my behalf?

Thanks!