GE frig cooling problems

Question

I have a GE TFX22P. Both freezer and fresh are not cooling. Frid side is in the 50 degrees. The repairman said it was not the heater defroster. No ice build-up. He said it was low on freon and might have a tiny leak. He put freon in it and it did get much colder but the refrigerator compressor and fan run constantly. Is that normal? Then he said after he put the freon in that the compressor tested poorly and I needed a new compressor. 500 dollars for the part. If freon worked doesn't that mean I have a leak? Why would I want a new compressor if I had a leak, or does adding extra freon cover up symptoms of a bad compressor. I am a woman ...lol. ....please help. I can't afford not doing the right thing. Should I buy a new frig? I am worried that I will blow money on a condensor and still have a freon leak. How long will it take for freon to leak back out? What should I do? Thanks so very much for any help. I need it badly