Would you divorce your spouse if...?

I don't believe that any of us ever know everything there is to know about anyone else. Not unless we torture them horrendously. I'm an open book to my spouse .. except about some things that are truly personal. Most people are. You don't mention what it is so that remains personal. People have the right to personal privacy. I can't think of anything my spouse could tell me now about something he chose to do/think/feel decades ago that would cause me to divorce him. I like who he is now!

I guess it would depend on the secret. 

Depends on what this great secret is. If someone admitted multiple homicide to me I'd have a hard time staying with them. But short of that and if it isn't criminal I can't think of too many things that would make me want to demolish a nearly 30 year relationship.

No I wouldn't even if she had had an abortion.

If the mistake were not disclosing the secret, that's one thing, but, if the mistake were breaking her silence, that's another matter. If 29 years went by uneventfully, then I'd be inclined to write it off and keep the marriage in tact.

Nobody can answer this without knowing what the secret is.  If it's something major that could impact the marriage, then it's a "lie by omission".  These can be the worst lies of all.  If the secret is that he/she has never liked your mother, I don't see why it would matter.

You’re being purposely vague. You know good and well that it depends on what the secret is

If the secret is that they enjoy the taste of Italian food? I think I’ll give them a pass.

If the secret is that they’ve murdered 26 people? That would be a dealbreaker. 

Etc. It could be a million things I don’t care about and a million dealbreakers. How can I know unless you say what it is?