Is there anyway to know if your private key is being used in multiple wallets/platforms?
For example, if I have your priv key and imported that into my wallet, will you be able to know about it? unless I make a transaction of course.
No, i believe you won't. Since i could have your private key in an offline wallet aswell, until i sign a message or make a rawtransaction with it, you should/could not know if it is compromised or not.
Some desktop/web wallets might automatically make contact with a node, but that still shouldn't reveal you using private key X, as far as im aware. ( Unless you sign a transaction ofcourse.)