How to i delete Messages on fb help?

[Kissing Raindrops]

I have been talking to my bf gf. He was a cheater and I found out and contacted her. She is heartbroken as I am. If I block her will she be able to see the old messages I sent her or if I deactivated my account will she able to see it. I don't wanna be a part of their world anymore I am tired I need to move on. He dated the 2 of us at once

[HazelP]

Sorry things are sucky for you right now

If you block someone on Facebook or deactivate your account, they should still be able to see messages. To delete one or more messages from a conversation:

Click Messages on the left side of your homepage
Open the conversation you want to delete a message from
From the Actions menu, click Delete Messages...
Use the checkboxes to select what messages you want to delete
Click Delete

You can delete an entire conversation by clicking Delete Conversation from the Actions menu. Keep in mind, once you delete your copy of this conversation, it cannot be undone.
Note: Deleting a message from your inbox will not delete the message from your friend's inbox.