Why is the antibonding pi bond higher in energy than the normal pi bond?
Firstly, the + and – signs you see do not indicate charge. They mark the sign of the electron’s wave function. In an atom, the electrons always have a negative charge, and the nucleus always has a positive one.

When a bonding orbital is formed, the electron density is concentrated in the area between the nuclei. The electrostatic attraction between the electrons and two (instead of one) nuclei, lowers the energy of the molecule. Furthermore, the electron density between the nuclei shields the electrostatic repulsion between the two positive nuclei to a certain degree.

In an antibonding orbital, the electron density is moved away from the internuclear area: the electron-nucleus attractions are minimized and the internuclear repulsion maximized. Thus, the molecule is destabilized.