No. If you send your bitcoins to anyone you lose them. He becomes the owner of those bitcoins.
No, If you sent bitcoins out the bitcoin diamonds (and other forks) will stay on the original address ( but if you give him your privatekey then he can get all the coins on that wallet BTC, BTG , BCH... all of them)
To sum up. PRIVATEKEY IS THE KEY TO YOUR COINS (all of them) ... so when privatekey is not compromised, you are safe.
That's different from what I heard. What about a replay attack? Can you explain how this happens? I just heard, that if you don't split the coin, then when you send bitcoin, someone can steal your forked coins or something like that. I'm really confused about this part. How that replay attack happens exactly
Indeed, because the transaction signature and hash will be the same on both chains.
Someone could then copy the signature + hash to spend the same amount on the other chain.
Lets say you have Bitcoin X and Bitcoin Y. Bitcoin Y just forked so all the UTXO's on Bitcoin X are also present on Bitcoin Y. ( Bitcoin Y has no replay protection).
You try to send 1 Bitcoin X to your exchange adress, that bitcoin X generates a valid hash + signature, ( for the transaction to confirm.).
Now that hash + signature will also be valid on the Bitcoin Y chain, meaning that anyone could copy it, and sent/transact your Bitcoin Y.
Note that the amount must be exactly the same ( otherwise the hash/signature would be invalid again.)
There's some interesting answers on how to prevent them here - >
https://bitcoin.stackexchange.com/questions/52210/what-is-the-best-way-to-prevent-replay-attacks-in-the-event-of-a-bitcoin-hard-fo/52260#52260