The poem "The Wanderer" is filled with imagery that depicts the isolation that the Wanderer feels as he traverses the sea looking for friendship.
In the very first line, it becomes known that the wanderer is, in fact, alone.
Often the solitary one finds grace for himself.
This is, by far, the most obvious quote from the poem which speaks to the fact that the Wanderer is alone.
Another quote which speaks of solitude is
Often I had alone to speak of my trouble each morning before dawn.
This quote speaks to the fact that it is a very regular happening that the speaker finds himself alone with his thoughts. There is no one around "with whom I dare clearly speak of my innermost thoughts" shows that all of the people with whom the wanderer trusted are gone. Again, this shows his solitude.
One last quote that speaks to the solitude the wanderer feels is
Then the friendless man wakes up again.
Again, readers can see that there is no one with whom the Wanderer can speak with.
As a side note, there are many references to "fallow", "decay", and emptiness. All of these add to the fact that the Wanderer simply has no one.