An answer is given by Tosfos Shantz, printed in the margin, in the name of Rabeinu Shimshon of Kutzi. Someone had relations with a married woman, so the child was a Mamzer. The son knew that as a Mamzer he will not find a wife if he stays in his home town, so he went to live in a faraway city. This man is similar to a Ger because he is a wanderer living away from home. He is also like an orphan since his real father will not admit that he is the father.

His mother is equivalent to a widow because she became forbidden to her husband as a result of the adultery. Consequently, she lives alone like a "widow" whose husband is really alive. (See Devarim 27:9, which not only mentions Ger Yasom but also mentions the widow.)

We learn from all of this that the person who committed adultery thereby created a Ger, an orphan, and a widow, all at the same time.

Our apologies for the inordinate delay in answering this question.

Kol Tuv,

Dovid Bloom