Is it possible for my ex husband to receive my message on his phone. Because I don't understand how he is finding out things he shouldn't know and relieving pictures sent to me that I have not sent to him. How do u stop this from happening.
Do you share an AppleID? More generally, does he know the password to your AppleID. If so, then yes, he can tell Apple that his phone (or Mac) is one of the places you want your messages to be delivered.
If that's not what you want, change your password.
This is likely to be a iCloud syncing issue. Assuming that you are using an Apple device (which is why you're here) then each photo you send/receive may be getting automatically backed up to your iCloud account. This might also be configured on another device (eg computer, iPad, iPod, etc.) that your Ex has. (Or maybe he set up your phone and you are using the same Apple ID.)
On an iPhone, you goto Settings > iCloud > Photos and turn off photo sharing.
If you go to www.icloud.com you will be able to see all the content he has been able to access and delete it.
Finally, as others above have suggested, you must also change your Apple ID Password immediately.