Give us some more details. What kinds of things has he said that makes you think he’s an occultist? Describe these dreams you’ve been having too. Generally, I tell folks to assume that the person they are weary of is not an occultist unless proven otherwise. It’s still quite rare to run across someone who does what we do here actively in the wild, unless you frequent witches covens and masonic lodges on the regular. However, I want you to take a look at this post and see if there are any similarities. This post came from a woman who was involved with a guy who had used magick from the Satanic Bible to make her obsessed over him. If you are under a spell, I imagine you will have a relatable experience.
Now typically, doing some kind of divination on the matter may help to figure out the truth, but this does require quite a bit of skill. Instead, my suggestion would be to call upon Sraagbel from EA’s Kingdom of Flames grimoire. He is a spirit of truth, and can help reveal hidden things in people. A sigil working with him may be all you need to uncover the truth.