How to know if someone is in your facebook?

[Kathia P]

So I have a feeling someone has been going into my facebook. But how do I know when or who logs in?

When I check login notification, I decide to test it myself. So I went on my phone and tried to login. The thing is, it asked me to validate my phone so I can log in and if I don't, it just gives my facebook a notification that some suspicious computer or phone tried to login to my account. I don't want it so we have to validate phones or computer. Is there any way I can find out when someone from a different location log in WITHOUT making it ask them to "Validate" their computer or phone? I want to find out who's been going onto my Facebook without them knowing that I know they are. Because I have a feeling that someone I know is logging into my Facebook. But if they see that it asked them to validate it, they'll stop logging in and I won't find out who it is exactly.

So when they're on and I find out about it, I can confront them and talk to them about it if it is indeed someone I know.

Another note: It doesn't say that they have an active session on my account, so that's why I believe they have been logging in and out after they check whatever they wanted. Not that I have anything important on it.

QUESTION: So, is there any way of being notified that someone has logged onto my facebook account, in a sneaky way without facebook asking to validate who logged in?
EDIT:

I know I can change my password- that's not what I want to do though. I'm 95% positive it's someone I know due to him knowing stuff that I talk with my other friends about but have no evidence.

So I want to actually find out if he IS the one logging into my account, so I can confront him about it and ask him how/why is he logging into it.

If I just changed my password, than I won't know why. Which is why I asked the question.

[Your Uncle Dodge!]

Change the password and make it so no one can just log in automatically. Problem solved.