The meaning of a long sentence. Thank you!
context:
Your friend James very shortly shewed himself the equal of his work, and what he did not already seem to know he learnt without effort and became so proficient as to excite the resentment of Mr O'Brien. So much were Mr Munro and your friend in each others company that I am sorry to record they became the butt of an ugly and infamous story, put about in the first instance by Mr O'Brien but then gaining general currency. I should not mention this, Sir, and risk offending you with ancient tattle, were there not certain repercussions that make the relation of even so unsavoury an episode pertinent.

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What does "I should not mention this, Sir, and risk offending you with ancient tattle, were there not certain repercussions that make the relation of even so unsavoury an episode pertinent. " Thanks, waiting for your help!

Question

The meaning of a long sentence. Thank you!
context: 
Your friend James very shortly shewed himself the equal of his work, and what he did not already seem to know he learnt without effort and became so proficient as to excite the resentment of Mr O'Brien. So much were Mr Munro and your friend in each others company that I am sorry to record they became the butt of an ugly and infamous story, put about in the first instance by Mr O'Brien but then gaining general currency. I should not mention this, Sir, and risk offending you with ancient tattle, were there not certain repercussions that make the relation of even so unsavoury an episode pertinent.

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What does "I should not mention this, Sir, and risk offending you with ancient tattle, were there not certain repercussions that make the relation of even so unsavoury an episode pertinent. "  Thanks, waiting for your help!

Answer

It means:  "Normally I would not tell you the gossip about Mr. Munro and James, but there are important reasons that I must do so."   It is not clear from the passage whether the speaker is actually reluctant to pass on the gossip, or is just pretending to be reluctant.  The gossip about an "unsavoury episode" involving two men may be that they were romantically involved.