What I could see is the reins are to short, your hands "to loud", aka to much movement, and you are sitting in the backseat of the car trying to reach the gas pedal in form.
All = you are fighting yourself.
Lengthen your reins, a soft bend in your elbow.
Your hands need to be where neck and wither meet as approximation of where they should look to be, then try fully extending your pinky above that part of the horses anatomy is about 4 - 5" at most, not half way up the neck is a gross exaggeration.
I was told hand height is even with your belly button at most whether riding western, English or whatever.
The further out your arm hangs the more motion your arm is going to have as it has no stability or strength propped in never-land.
As for your posting...you need to scrunch your butt forward in the saddle so your crotch is touching the sweep up of the pommel...
I think either your saddle is to flat, your saddle is tilted down and back, it is to large for you or those combined and then some more..was hard to see clearly at such a distance of filmed.
You though have your legs propped way out in front of you, called a "chair-seat" then need to haul your body up and out of the saddle and doing that, yes you are using the horses mouth for balancing, hence he is not happy is accurate in your assumption.
Your instructor needs to get you better positioned where to sit in the saddle to offer you support and help and I bet much of your horses displeasure shall disappear, you will be more comfortable and able to easier ride and control with less effort on your part..
Your basics need some fine-tuning and practice..once you though get your body where it needs to be I think the rest is going to suddenly make sense and be easier for you to ride and communicate with your horse quietly.
Horse is a nice animal and has a caring rider who knows some tweaking needs done, a work in progress and for one who hasn't ridden much in the past year...not bad, not bad at all!!