Facebook- A Question

This is not perhaps a philatelic question but it does touch on it for me.
I do not use Facebook for much so am unfamiliar with all its ins and outs. I do have to use it however to post comments on some websites I belong to. Every time I post using my Facebook account then go back later, my comment is not there. I somehow doubt I am being singled out for deletion by these sites. Is there something in Facebook that prevents a poster using them to view their comment later? This is driving me nuts!

I think this is a question for Facebook.

The person you are leaving a comment to can choose to delete that comment you are posting on his/her page.

once the comment that has been sent, the person that you sent it to can only edit the comment. if they choose to keep it or not ( as a member has mentioned already )