William Shakepseare's "Sonnet 104" speaks to his view on friendship (or at least his narrator's view on friendship). This sonnet illustrates the timeless nature of friendship for Shakespeare. Although the sonnet has been regarded as a love poem between Shakespeare and the Earl of Southampton, it still illustrates the great importance of a friendship.
For Shakespeare, friendship is eternal. The first meeting with his friend is as fresh in his mind "three summers" later. For him, real friendships stand the test of time.
Another point which needs illustration is the fact that winter can shake "the foliage." In one way, winter could refer to conflict which could exist between friends. That said, the strength of the friendship can survive anything (given the fact that spring (rebirth) follows winter).