A few thoughts:
You seem to go back and forth on whether you're upset by the possibility that he would feel hateful thoughts vs the possibility that he would express them. Maybe it's both, but I wonder if it would be helpful to think about them separately.
To me it seems like you can imagine him hating you because you think you saw a glimpse of it. Do you think it could help to have him explain more what his emotions were like during that past fight, not focusing on the topic of the disagreement but on his experience of the emotions, so you could understand it better?
I remember when my son was small(er), there were times that I was so furious with him that I felt that I hated him, and that during such moments it was impossible for me to be aware of love as well. This surprised my husband, who was still aware of love even in his moments of anger, and it disturbed him a bit too. Perhaps he thought I could not truly love my son and feel this, but I did. Perhaps this is a little parallel to your situation?
You mention insecurity, as if the fact that he can feel something that looks like hate means he doesn't actually love you; the alternative may be that he feels so strongly for you that the idea of loss is more than he can deal with, and his response is anger.
It reminds me of parts of a book I read recently, called "Mistakes were made (but not by me)", on how we tend to defend ourselves against things that make us feel bad. (The author wrote a interesting book on anger as well). If you stay really stuck on this idea maybe it'd be something to explore.