f all his messages to you have disappeared it sounds like you might had accidentally blocked him. No she sees a message and when she clicks to view it the contents are blank. So he is not blocked or anything. The message is there. She can see it in her inbox. When she tries to view the contents are blank. This has been complained about a couple times.
If all your messages to him disappeared but his remains it sounds like he blocked you.
Check your blocklist to see if his name is there.