Re: Can someone have my private key ?

If you create a btc address you get the private key of that address, what if this address is already in use ?

if it does happen, which very less likely to happen in your lifetime, it is called an address collision
read this https://en.bitcoin.it/wiki/Technical_background_of_version_1_Bitcoin_addresses#Collisions_.28lack_thereof.29

I know there is a really low probability but this can happen, am I right ?

It is more likely that the Earth is destroyed in the next 5 seconds, than that a collision occur in the next millenium.

there's a group of people in the project which attempt to generate address collisions
they are called Large Bitcoin Collider there is also a thread about it https://bitcointalk.org/index.php?topic=1877935.0
you can join them and try it yourself how to do "address collision"