What happened to Len Fenerman's wife ?

Abigail asks Len how his wife died. He tells her she committed suicide.

The suicide of Fenerman's wife is an important tool of Sebold's in presenting her feminist views.

Sebold is using symbolism to say that marriage is the death of the woman - aka. Fenerman's wife is dead. It is important to note here also that the wife is referred to only as "wife" which strengthens this indication at the death of the woman.

This is supported also in what we see of Abigail. In order to save herself from this fate, she has an affair with Fenerman and leaves Jack. Effectively, it is just Sebold expressing her extremist feminist views.