if everything came from the big bang, and the big bang before it exploded was so dense, then why didn't it collapse into a huge black hole?
This seems to be something that comes up quite a bit, but it is a good question, none the less.
I’m going to copy & paste this answer because what I typed up was three times longer than this simple one-paragraph explanation:
“The short answer is that the Big Bang gets away with it because it is expanding rapidly near the beginning and the rate of expansion is slowing down. Space can be flat even when spacetime is not. Spacetime’s curvature can come from the temporal parts of the spacetime metric which measures the deceleration of the expansion of the universe. So the total curvature of spacetime is related to the density of matter, but there is a contribution to curvature from the expansion as well as from any curvature of space. The Schwarzschild solution of the gravitational equations is static and demonstrates the limits placed on a static spherical body before it must collapse to a black hole. The Schwarzschild limit does not apply to rapidly expanding matter.”
When you have the time to read further, you can look into Is the Big Bang a Black Hole? which explains, in detail, the differences between the Big Bang and black holes. I hope this helped you out some!