Sorry to hear. Are you British? If so, read below.
Your spelling doesn't indicate which side of the pond you're on. Potential cases of involuntary commitment vary from one US state to another.
You use the term "medical guardianship". Tends to be something referred to by the Brits. If so, are we to assume you are referring to provisions of the United Kingdom's Mental Health Act of 1983?
Has anyone used the term "sectioning" to describe your predicament?
"Involuntary mental guardianship can be related to "sectioning," which refers to the legal process of detaining someone in a hospital for assessment or treatment under mental health laws. This process typically involves being sectioned under specific sections of the Mental Health Act, allowing for involuntary treatment when necessary."
If so you can argue over the process in your own behalf, but it appears that it would involve an appeal to "mental health tribunal" with the option of seeking legal counsel for advice and support from a mental health advocate.
That's about as far as I can help you given I am not British. Where it appears you'd be dealing with a different medical bureaucracy and legal system to contend with. Though if this all seems to be the case with you, I could understand your boyfriend's frustration and apprehension where he likely cannot look out for you on his- or your terms. However if your boyfriend isn't willing to assist you in such a fight, that should be the best indicator to dump
him.
Sadly that your personal freedom is at stake. A much greater concern for you than anything regarding relationships whether you deem things fair or not.
https://www.mind.org.uk/information-support/legal-rights/sectioning/about-sectioning/