Lemme guess, in the 1st timeline, bietch Angela had done something to Cassiel, maybe charming magic or drug, just remember the tea her maid Rona used to serve Jayne in previous chapters (Jayne later spat in out), they definitely put something in it, so i think Angela and Rona drugged Cassiel, making him fall for her because she wanted to steal Jayne's man or perhaps she want to be the future duchess. But in this timeline, she is aiming for the 2nd prince who possibly becomes crown prince and can ascend the throne (future emperor > future duke), so she just lets Cassiel go.