I also think that Sonnet 123 which is written to Time, also gives a great image of the stability of love by comparing it to the pyramids. He will defy time and be true to love " despite thy scythe and thee." Time's scythe of course is death and Shakespeare's love will last beyond it.
In a different way, I think Sonnet 130 also gives an image of love's stability. Here, Shakespeare is saying that his love looks, sounds, and smells nothing like the romantic ideals of his age,"and yet, by heaven, I think my love as rare/as any she belied with false compare." Shakespeare says his love for this woman is stronger and more lasting than any flowery false comparisons he could make about her. He is not going to follow the fashion of romantic love. There is more to this woman than her external changing characteristics and this unchanging part of her is what he loves.
There are a number of images of true love's stability in the sonnets. Some of them deny its stability; some celebrate it.
The two most famous are probably found in sonnet 18 and sonnet 116.
Sonnet 18 starts "Shall I compare thee to a summer's day?
Thou art more lovely and more temperate"
and ends with "
So long as men can breathe, or eyes can see,
So long lives this, and this gives life to thee. "
These claim the beloved's beauty does not change like the seasons, and that the poet's love will outlast time and vision.
In sonnet 116, Shakespeare says of love "It is the star to every wandering bark," saying that love is so steady you can steer a boat by it.