Needed: Plausible explanation for Facebook password reverting back to an old password?

Here's the situation: I was suspicious of my boyfriend's behavior so I tried to get into his Facebook account. I knew the password for his email and I also knew his previous Facebook password before he changed it. So I got into his email and had his password reset to his previous Facebook password. I want to come up with a plausible explanation for why that would happen without him getting suspicious of me. I didn't really change anything in his profile so really the only thing he would likely notice is that the password is not the one he was currently using. I want him to be able to resume use of his Facebook account without him thinking that someone hacked him because then he'll be suspicious. What is a plausible explanation I can use if he asks? I was thinking of maybe telling him it was a temporary glitch that got fixed so hopefully he'll buy that and drop the subject but I want other ideas just in case.

Okay ... Here's a plausible explanation:

"I don't trust you.  I used your email to request the password change, so I could monitor your Facebook account.  But now I realize it's better to just break up with you, because I don't trust you."

Don't lie.

I gather you didn't find what you was looking for? Ah, deceit the foundation of every stable relationship.  Tell him the truth before you bury yourself in that hole you are digging.

You are busted! You did something out of spite without thinking and now you want US to fix your deceptive ways?!?! I don't think so. Tell the truth and face what is coming your way! There ARE consequences to actions you know.....

Here's one. Tell him this one word for word.

"I am a girlfriend who lacks trust in you. I hacked your email and your Facebook. I will understand if you want to breakup with me, as I would feel the same way of you did this to me." 

In other words, grow up and take responsibility for your actions. You also may just want to break up with your boyfriend now, as this behavior is not something that promotes a long term relationship.

Plausible explanation that you can tell him .. "it happens !"

.. Then you can further explain "because I am that kind of girl Who is untrusting, suspicious and has no respect for your privacy " .. "who instead of asking to share and have an open and honest relationship would rather go behind your back and break your confidence"

He deserves to know exactly what happened.  If he's still interested after that, you might be able to earn his trust over time.