what is the difference between inter-dependency and co-dependency?
At the word level "codependency" involves two objects while "interdependency" multiple objects.

If you are referring to specific meanings in some discipline, you will have to be more precise in your question.

Actually I read in an article that co-dependency is not good for a marriage though interdependency is..
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Interdependency has a more general meaning and is used in fields as diverse as economics and biology. Simply put, it means a state of being mutually reliant (dependent) on one another. It has a neutral to positive connotation.

Codependency is a term specifically used in the field of psychology/counselling. It refers to the state of one person being dependent on another to the extent of negating one's own needs. It has a negative connotation.