Electrons in bonding orbitals stabilize the molecule because they are between the nuclei.
They also have lower energies because they are closer to the nuclei.
Antibonding orbitals place most of the electron density outside the nuclei.Antibonding orbitals place less electron density between the nuclei.
The nuclear repulsions are greater, so the energy of the molecule increases.
Antibonding orbitals are at higher energy levels than bonding orbitals.