My car won't start without a jump. I’d jump it with cables, it will start with no problem, but as soon as I turn it off, I won't turn over.
That sounds like an empty battery. Now the question is, is the battery just empty or is it in need of replacement.
After jumpstarting, you should drive the car for about half an hour-45 min. That's enough to charge the battery. Then stop the engine and try to start again. If the engine starts, chances are the battery is still usable. If it doesn't, it's time to replace the battery.
How much do you drive it? It takes a while to charge from being totally dead, but batteries don't like to go dead, so by now, you may need a new battery.
One thing to be aware of is that the alternator is not designed to charge a dead battery; it's designed to keep it charged with daily driving. Using the alternator to charge the battery can eventually burn it out due to overheating.
What you need if you don't drive often enough to keep the battery charged, or if your battery goes dead, is an external charger, like a trickle charger, such as the "Battery Tender" brand. I got one at Costco for $35, and it can charge a totally dead battery in several hours. Much cheaper than a new alternator.