Removal of access to my iCloud account.***

Logging into your Facebook just requires a Password to your Facebook account and is not the same as your iCloud account password (at least it shouldn't be). To prevent unauthorized access to your Facebook account, you would need to change your Password there and don't use a password that you have used for any other service.

For someone that is signed into your iCloud account, you will want to follow these steps in order:

1-- View and change any Trusted Phone number that is not yours.

About trusted phone numbers and trusted devices for Apple Account - Apple Support

2-- View the devices that are signed into your Apple Account by going to Settings > [name on top] and scroll to the bottom to view what is signed into your account. If a device owned by your ex is not there, they are not currently signed into your account, but you still still proceed to step 3.

3-- Change your Apple Account Password. If asked to sign out of all other devices, you should do that.

Change your Apple Account password - Apple Support

I have someone who has access to my iCloud account. How can I remove them?

Brookethfffff wrote:

My ex is on my iCloud account and I need to remove him. He is stalking me and logging into my facebook

[Edited by Moderator]

Look here If you think your Apple Account has been compromised - Apple Support

Suggest changing your password and enabling 2FA for everything.

Worrell_T60 wrote:

I have someone who has access to my iCloud account. How can I remove them?

Please read the information that has already been provided to the user you have replied to and then describe what has not worked for you. So far there are only 2 other posts that contain the solution, but a thread can become difficult to navigate if everyone just posted the same question without reading the information that has been given. In some cases it is better to provide your own post with your specific information, so each user gets individual attention for any follow up questions.