Cupid always keeps his gun around
Cupid makes people fall in love by shooting them with arrows. G is saying Cupid is on his game and it’s easy to fall in love even when it’s a bad idea.
Looks like Cupid wants to keep up with modern weaponry. The Cupid moving up to guns motif is one that G has used before in Apple of My Eye which was mentioned in the line previous to this one.
To help improve the meaning of these lyrics, visit "Runaround Sue" by G-Eazy (Ft. Greg Banks) Lyrics and leave a comment on the lyrics box