My Nitrite was high, one of my glo fish died.

[Andy Sager]

...I just wounder when i can sit back and enjoy my fish. ...Keeping my fish a live is a hard task. I wounder why my fish die, when I make sure the water is safe for my fish.

To answer your first part, when you stop pushing the limits.
To answer the second part, Yes, it can be difficult when you push the limits. Just because a tank can hold 10 fish does not mean that you should put 10 fish in it and expect things to go smoothly. Overcrowding a tank leads to either A) more work on your part. B) shortened lifespans of the fish. C) lowered resistance to diseases and parasites. Can it be done? Yes, it just takes more work. While Aiken is working with numbers, my calculator shows that ammonia coming from the fish, the food and the water is greater than ammonia that comes just from the fish and the food. A properly balanced aquarium should have 0 ammonia, 0 nitrite and little nitrate ( as little as possible. ) There are ways of combatting nitrate that are not from water changes, that include nitrate loving live plants or using nitrate absorbing matrixes in your filter. You need proper lighting for the plants ( some use more, some less) and the matrix I like the best is the Polyfilter pad (poly-bio-marine.com ) for the filter. Both cost extra money that you would not have to spend with a properly stocked aquarium.
In reality fish keeping is not really hard. It is a bit more complicated today than it was say 20 years ago ( which by the way, was more complicated than when I started 50 years ago) due to changes in the water chemistry from city waters and a lack of good information that applies to you ( the general you not the specific you). I get my community tanks to the point where they get fed 3 times a day and maintenance once a week. That's done by understocking and feeding properly.

 

[Andy Sager]

Here's a page you should read through as they are one of the better magazines for the hobby these days. https://www.practicalfishkeeping.co.uk/features/39-top-tips-for-fishkeepers/

 

[Aiken Drum]

Changing water to keep nitrate at zero is excessive. Keeping nitrate below 20ppm is a good place to be. Many people keep fish just fine at 40ppm or even higher. If you are having to do more water changes than one 50% water change per week to keep below 40ppm then it is a clear sign that reducing the number of fish, or getting a bigger tank would be a good idea.