Marriage has been designed to be for life for many good reasons:
Marriage ...
Enables the couple to share on intimate and private matters that can not be easily shared elsewhere.

I would have just used share instead of share on? e.g. You can share everything with me from your personal matters to financial troubles.

The Dotens have a deep conviction that marriage is for life.

Is Dotens a family name?
What does the phrase marriage is for life mean?
Yes, or the name of the tribe or a religious sect:-)
For ever, for the duration of the life.
And yes, you are right about not using "on" as well.
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