It is really hard to break the anticipation habit, but trust me, it can be done!
I used to tell myself 'Ok he already spooked at that so he knows it's there'.
Maybe you could try some Rescue Remedy for yourself?
I would sing a song in my head or chant something like 'calm, relaxed, calm relaxed' and keep breathing!
Maybe try doing yoga before riding. :)
I know I sound all hippy dippy, and I'm really not!