The separation of the P-wave comes from spin-orbit effects. As for any level different from a s-level whose orbital quantum number vanishes.

Concerning the orbit stuff, you may want to see the model as neutrons and protons orbiting around the center of the nucleus. Thanks to Pauli exclusion principle, they will never collider (as all the lowest energy levels are taken, there is no way for them to jump to another state without an external source of energy).

PS: thanks for the typo ;)