A person's circumstances do not remain the same forever. There are times of ease and times of hardship and illness. According to Islamic teachings, helping someone who is sick or struggling, and making every effort toward their recovery and betterment, is an act of great reward. And if that person is connected to you through a family or marital bond, you can hope for double the reward. A truly good person is one who helps others and does whatever they can to benefit those around them.
In the situation you have described, if you support your husband by arranging his treatment, take every possible step toward his recovery and improvement, and exercise patience over the difficulties and pain you receive from him, you will be greatly rewarded for this, and your standing before Allah will be elevated. Insha'Allah, your husband's condition will begin to improve before long.
As for the pressure from your parents, they cannot force you into seeking khula'. That decision belongs to you alone.
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دلائل:
صحيح ابن حبان: (رقم الحدیث: 2908، ط: مؤسسة الرسالة)
أخبرنا أحمد بن علي بن المثنى، قال: حدثنا محمد بن العلاء بن كريب، قال: حدثنا يونس بن بكير، قال: حدثنا يحيى بن أيوب هو البجلي، قال: حدثنا أبو زرعة، قال: حدثنا أبو هريرة، قال: قال رسول الله صلى الله عليه وسلم: «إن الرجل لتكون له عند الله المنزلة، فما يبلغها بعمل، فلا يزال الله يبتليه بما يكره حتى يبلغه إياها».
الدر المختار: (501/1، ط: دار الفکر)
ولا یتخیر أحدهما أی الزوجین بعیب الآخر فاحشاً کجنون وجذام وبرص ورتق وقرن۔
Allah the Almighty knows best.
Darul ifta Al-Ikhlas, Karachi.