To amplify what others have said... the word "fix" is an example of a short, common English word with an unusual number of completely different meanings. I know the meaning, but I checked a dictionary to see what it would say. It listed found eighteen meanings for the word--nine uses as a transitive verb, three as an intransitive verb, six as a noun, plus three phrasal verbs. One of them is: "Slang: An amount or dose of something craved, especially an intravenous injection of a narcotic."

'fix' is like if you were taking drugs, you would want to get your drug 'fix'. Also, diary of a wimpy kid? Lol

The other comments are right, but to expand on this context... it means the person has a certain amount of entertainment they want to enjoy. Once they reach that amount, it will "fix" or "fill" their entertainment desire.

It means watching TV is like a drug for this person. A fix can mean taking drugs.

Something that you’re addicted to