"might do sth." vs. "might be doing" vs. "might have done"
Grammar, sometimes, is a mystery. My friends & I discussed one of it for a long time yesterday evening,but still have no idea.
Here is it:
What's the difference of next three:
1 might have an affair
2 might be having an affair
3 might have had an affair
and, why, in BBC's Sherlock,there is "I think my husband might be having an affair. "? But not "I think my husband might have an affair."

Thank you very much for any reply. thank you!

But here still the question:
Can we say "I think my husband might have an affair." instead of "I think my husband might be having an affair. "? They're the same?

Question

"might do sth." vs. "might be doing" vs. "might have done"
Grammar, sometimes, is a mystery. My friends & I discussed one of it for a long time yesterday evening,but still have no idea.
 Here is it: 
What's the difference of next three: 
1 might have an affair 
2 might be having an affair 
3 might have had an affair 
and, why, in BBC's Sherlock,there is "I think my husband might be having an affair. "? But not "I think my husband might have an affair."
 
Thank you very much for any reply. thank you!

But here still the question:
Can we say "I think my husband might have an affair." instead of "I think my husband might be having an affair. "? They're the same?

Answer

1. Future possibility - It may/might happen in the future
2. Present possibility - It may/might be happening now
3. Past possibility - It may/might have happened in the past

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