If you don't want to write an emotional review (which I can understand as I don't think I would) maybe give it a couple of weeks and email him explaining why you are terminating and go into how it's left you feeling, but not from an emotional place (if that makes sense). Rather like writing a complaint, you could explain from your logical mind how this has left you to get it out of your system. You probably won't get a reply and could even say you don't want one, but write it for closure. He's more likely to take something from a clear logical email rather than an emotional one. It's an approach I've taken when writing letters of complaint to various companies etc. The impact is greater if I don't write from my emotion, but state the emotion clearly.