This molecular geometry and bond angle can be understood based on valence shell electron pair repulsion (VSEPR) theory. In SiS$_2$, the central silicon atom (Si) is bonded to two sulfur atoms (S), each through a double bond. Silicon has four valence electrons, of which two are involved in double bonds with each sulfur atom. This leaves two lone pairs of electrons on the silicon atom.
According to VSEPR theory, the arrangement of electron pairs around a central atom will adopt a geometry that minimizes the repulsion between them. In the case of SiS$_2$, the two lone pairs of electrons on the silicon atom are oriented as far apart as possible to minimize electron-electron repulsion. This results in the bent molecular geometry with a bond angle of approximately 119.5 degrees.
The angular or V-shaped molecular shape of silicon disulfide is influenced by the repulsion between the two lone pairs of electrons on the silicon atom and the bonding pairs of electrons involved in the double bonds with the sulfur atoms. This arrangement leads to a distorted tetrahedral electron-pair geometry around the silicon atom, giving rise to the bent molecular structure.
