If she talks to him more than she talks to her own husband, it's inappropriate.

If she tells him things that she would not be comfortable with her husband hearing, it's inappropriate.

If her husband is uncomfortable with it, then it's inappropriate.

For add'l reading, the book "NOT Just Friends," by Shirley Glass, is considered the definitive work on EAs.

Puppy

P.S. 1400 text messages, is inappropriate!!!