I can see you are a little defensive but let me give you some insight as to why some of us are defensive: Many of us have been riding and training for years, I myself have been doing it for 15 years and that is nothing compared to many of my fellow members. If there is one thing that really irks me, and I suspect anyone else that has trained/re-trained horses for others over a period of time, it is hearing a person blame their horse for ANYTHING. Many of the posts I believe were trying to illustrate this point to you and in type it perhaps it came across a little harsh. Take it as you will but rest assured that no-one is trying to offend you, they are just coming from the other side of the fence.
While I absolutely agree with this, it sounds at this point Serafina that you aren't quite ready to deal with the behaviors this horse is presenting you. I think it would be wise of your instructor to get you on a horse slightly less challenging and work on the skill set needed to deal with one as challenging as your current lesson mount.
Has your instructor gotten on this horse during a lesson or another for that matter and demonstrated hands on how to work through his quirks? I always ride one of my training greenies while giving lessons as it presents a greater opportunity to teach working through problems should they arise.
I've been dealing with a similar situation with my hubby. I've been logging some serious re-habbing hours on "his" mare and have gotten her coming along fabulously. I can pretty well do anything I want with her using just my seat and legs, pivot, sidepass, stop on a dime. She's very tuned in. The problem, hubby rides her and she works like a drunken sailor. He has extremely muscular calves and his legs are very on without him needing to try to ride legs on. He has yet to find the balance in his legs to keep her between them and with the slightest varying pressure she is kinda all over the place for him. He got fed up and was ready to throw in the towel and started blaming the mare (though he has seen her work flawlessly for me first hand) and had taken to calling her "Lucifer". So for the last few weeks he has spent time riding my older mare who is very much more tolerant of his unintentional misguidance. He has found more balance and improved greatly on keeping one between his legs. He rode his mare last night and got her to ride straight lines and made a perfect square. He said "Wow, never thought that would happen. Now I see that it was me, I kinda like her."
Don't give up, look at both yourself and the horse and figure out where the miscommunication is happening. It sounds like a crop could be the variable & if that is what it takes to get him working, approach your instructor about learning to ride with a crop on a more seasoned horse and then go back to the challenge.
Regardless of fault on the part of rider or horse, lessons should be enjoyable and at this point it doesn't sound like they are in the least. Have a sit down with your instructor, discuss how you are feeling and what you both need to do to get you back to having fun with your lessons. Good luck!