Fluorine forms one bond. Fluorine has five electrons in its p orbitals. By gaining one more electron, it fills the p orbitals and becomes stable. Therefore, it only forms one bond.
Atoms are more stable with filled orbitals. They tend to follow the octet rule, which states that atoms are more stable with eight electrons in their outermost shell. The number eight comes from two electrons in a filled s subshell and six electrons in a filled p subshell. Fluorine, with seven valence electrons, only needs to accept one electron to satisfy the octet rule. This is why it only forms one bond.