There are many ways - keyloggers, guessing the password, watching you type.
It's not hard to figure out your password- if he has access to your computer! All he has to do is go into tools, options and look for it there..... it has all your saved passwords for anywhere you have one. Its in the 'security' tab of the options... nothing covert about it.... just change it and dont save it... also use a capital letter and a number set that he wouldn't think of normally as associated to anything you would-
hey-- I've hacked into your Facebook account.
If he has access to your computer he probably installed a keylogger.
Or else he guessed your password.
May be you use the same password for all the accounts or its something he knows about and was able to guess it. Change you password and select something that you normally wouldn't
You have a ****** password.
Maybe he installed a keylogger.
Or watched you type your password.
Or is psychic.
figured out ur password