What does this phrase mean?

When some people talk about money, They speak as if it were a mysterious lover, Who went out to buy milk and never Came back

The phrase means that people talk about money as something they have no control over but they do.

Explanation:

The phrase is describing the habit of people that they talk about the money they have or the money they spent or lost as something they had no control over or was something mysterious to them.

The tone of the line suggests otherwise.

The tone of the line suggests that the person that is saying the phrase believes that that cannot be the case and the people have control over their money and how it goes out of their hand.