how do i retrieve text messages i accidentally deleted?

They are gone.

Then you are in the wrong place, bacause Apple has no such tricks available. You need to be searching the net for 3rd party SMS recovery software.

Here is one;

http://www.wondershare.com/disk-utility/iphone-sms-recovery.html

Try sending a new text to the same person. See if the deleted ones show up in the conversation.

I have never seen that happen, have you?

I'm pretty sure (not positive) it's happened to me several times. I've not seen it confirmed on here, although I've only recommended it 2-3 times.