賺來 or for another example 贏來 are both phrases that mean "to earn back.." or "to win back..". In Chinese, we actually would also say "賺回來" or "贏回來" , which are easier for you to understand.
"一次就" here is an adverb. The sentence still makes sense if you just say "你忍心把我辛苦賺來的錢吃光啊?", and adding "一次就" is to emphasize what you said "in one shot". Since we use adverbs to express "the emotion or condition while doing something" in Chinese , they are often placed in front of verbs.