When Paul says, "my true companion," the word "you" is singular. Paul does not say the name of the person. He calls him that to show he worked with Paul to spread the gospel. (See: [[rc://en/ta/man/translate/figs-you]])
This metaphor is from farming, where two animals would be bound to the same yoke, and so they work together. Alternate translation: "fellow worker" (See: [[rc://en/ta/man/translate/figs-metaphor]])