For those mad at Cassiel, in chapter 7 we see that in their first meeting he is drinking tea with them, and curiosly no one else in the room is. We focus a fair bit on the tea cup, and after that he is infatuated. This time around, however, Rona was fired in chapter 6, so she wasn't around when Cassiel came to visit. And also Angela had already set her sights on someone better.
So I'm thinking he was a victim of Rona's "love potion", and brainwashed. I'm willing to cut him some slack based on that. Sucks for him that Jayna already dumped him.