I wrote a big long answer to this yesterday, but I deleted it because this sounds like a religious discussion to me, which I thought was against the rules, but since it doesn't seem to be going away, here's the gist of it.
The sun's energy source is its weight. It's a solid mass. Find a picture that shows the size of Earth relative to the size of its star. That's how much energy it has. Better yet, try this: Jupiter has almost enough mass to cause fusion by its own gravity. Now, compare the size of Jupiter to the size of the sun. The sun is much larger than Jupiter, and so the sun has far more mass than it needs to cause fusion.
The sun's fuel source is the massive amount of hydrogen that it's comprised of. The sun only burns on the surface. It's definitely hot, and that heat would cause it to be molten were it not for the fact that it's so heavy on itself. Though it's the weight that causes the heat to generate, which causes the fusion that ignites the hydrogen on the surface.
Also, the weight of the sun is what's causing it to be compressed into as small a size as it is. The sun is much more massive than it appears. Were the sun to lose weight, it would grow larger. That is happening, perhaps in simplistic terms. As the sun burns hydrogen, it grows larger. By the time the sun has burned enough hydrogen to begin to stop the fusion process, the sun will have grown so large as to approximately encompass Earth's orbit. That means the sun is extremely huge, and has that much energy to burn, which actually takes billions of years because of the vast quantity of energy stored in it.
By the way, one of the key roles being played here is the law of gravity. The more massive an object is, the more gravity it has. The sun is many times more massive than Earth, and therefore has many times stronger gravity than Earth. There is no structure in your body strong enough to stand on the surface of the sun, even if it were a cool enough spot. The atoms on the sun are actually being squished together by its gravity. That's fusion. That's nuclear energy. That makes the sun hot and ignites the hydrogen, which makes the sun bright.
Our sun is kind of on the smaller side when it comes to suns, which means it doesn't have as much weight, and therefore not as aggressive of fusion taking place, which means its supply of hydrogen will last longer than larger stars. This has the added advantage of allowing the sun to grow as it loses weight, and eventually stop the fusion process. This means that when the sun runs out of hydrogen, it won't be expressed with massively hot energy blowing itself outward, causing itself to collapse on itself and explode. Our sun won't explode. It will just grow dim, and finally shrink to a tiny ball. Tiny .. uh .. still quite a bit larger than Earth. The sun should have enough hydrogen left at this point to be able to support life on Earth for about another 4 billion years.