My brother could not help but _____ at his condition. Fill in the blank with right form verb:

Cannot / can't help but - to be unable to refrain from or avoid; be obliged to.
এর পরে verb এর base form বসে।

Example sentence:
Her parents live nearby, so she can't help but go there on holidays. 
Bob is a tennis fan and can't help but travel to Wimbledon each year.

কিন্তু,
Can't help এরপর verb + ing হয়।
Example: He cannot help telling a lie.

Can't but এরপর verb এর base form বসে।
Example: She could not but congratulate him. 

Source: Oxford Dictionary & Collins Dictionary.