Can I get copy of all text messages between my ex husband and I

Have you checked your carrier's web site to see if the text messages are there?

If you were syncing Messages with iCloud, if you have access to another Mac device/computer, you can sign into Messages using your Apple ID, and they should download.

If you weren't syncing with iCloud and you have a current backup, you can restore that to another device.

so then how would you be able to move all those messages to a single file? ( ie. i dont want to cut paste hundeds of times)

thanks!

You are welcome. I don't know of a way to do that except by cut and paste.