Apologies for the delay in my reply. This may not be the answer you were hoping for, but it may be the answer to take your son forward. I understand that your son is bright and has chosen his own subject, which requires lots of time and effort. However, I also hear that, as caring parents, you have cajoled and forced (your word) him to do better along the way, no doubt with good and positive intentions that he gets a good education and a good job, so that he can have a comfortable life, which is what we all hope for four our children. Yet I would question 2 things here, and maybe they are related. In order to 'keep going' at something that is tough, it is important to have some levels of internal motivation, rather than external, ie. it needs to come from within the self, rather than from parents or teachers, etc. If the main motivation to do so much hard work comes from an external source, then eventually it will run out. This is because the benefits also become external - I'm doing this for someone else and not me. I wonder whether, one and a half years ago, this 'phobia' was a fear of letting someone (you as parents???) down if it doesn't go well? (I am only guessing, this is a theory based upon what you have told me). The situation then becomes very 'stodgy' for him - the work is hard, he is not self-motivated and the benefits are (perceived to be) for someone else. Maybe he is working out his frustrations now on a daily basis in sport.
If the above is true (and it may not be), then it is possible that your son does not even realise what is going on and may be as confused and concerned by his lack of wanting to learn as you are. Therefore if you ask him about this, he may simply deny it. My advice to you would be to show no concern, as hard as this may be. The consequences of this, over time, would be that your son becomes more and more aware of the consequences of 'not getting on with things' for himself - in some ways, you are his scapegoat - you tell him he must do well, he tells you everything is fine, and this supports his belief that 'everything is fine' when the reality is that all is slipping away from him. You need to allow it to slip without saying anything to him, so that he can see it is slipping without you to be strong for. Then your son can see clearly - this is my life, it is my future, if I work at it, the consequences are for me, the benefits are for me - no-one else. Yes, my parents will be proud - but I am doing this for me. If he chooses to let it all go, then that is his choice and he must suffer the consequences - it's one of life's lessons. Do you see? He cannot do this for you, or his dad, or anyone other than himself. he needs to find his own confidence, his own motivation, his own strength. I'm afraid it's called 'tough love' and it is indeed very tough. You and your husband (or partner, or whoever you have to support you) need to find support and solice in each other and let your son become the person he is going to be. Let the bird out of the cage and he will fly alone - if he dips, he will learn to soar again. I hope this is useful for you. Please press accept if you find my answer valuable. Happy to respond but it will be tomorrow. It is getting late now in England. Be strong, With very Best Wishes, Sarah