Why would you think he might become violent? Has he shown any behaviours that indicate that he might?While it can be possible for almost anyone to become violent if they are pushed, including nacissists, not all do. I would be watching his behaviour more than looking at the diagnosis (or lack of). Has there been anything that has made you afraid he might hurt you? There is a big difference between getting annoyed and becoming angry enough to become violent.

The most important thing is keeping yourself safe. If you think there are signs that he is becoming violent then make sure you get out and care for yourself.