The extended metaphor in the sonnet suggests that 2. Love is only true if it is unwavering in the face of adversity, like the unmoving position of a star in the sky.
In this sonnet, Shakespeare presents love as a constant and unchanging force that remains steadfast regardless of challenges or changes in circumstances. The imagery of the "ever-fixed mark" and the "star to every wandering bark" illustrates love's reliability and consistency, contrasting it with the fleeting nature of physical beauty and time. The idea is that genuine love endures all trials and remains unaltered, serving as a guiding light, much like a star for a ship at sea.