From dictionary.com there is the two-syllable “dahy-mun nd” and the three syllable “dahy-uh-mun nd”.
How do you personally think you say it? I think I actually do the three syllable version of the word.
I say “die mun”. 
“Die-mund”
Marriage, 2. 3 if you really emphasize the ge.
I say 2 syllables for diamond.
I also say diamond in two syllables.
2 syllables.
Two: “DIE mond.”
But it’s spelt “Throatwobbler Mangrove.”
2 syllables. A cross between “dime un” and “die mun.” I can’t think of anybody I know who pronounces what would be the -a- syllable, unless it’s some pretentious radio or TV announcer. They’re the kind who make “every” a 3-syllable word.
2 syllables.
Three syllables.
“I’m sor-ry.”
Sometimes five.
“I’m ver-y sor-ry”
Assuming the first syllable is accented, that’s exactly how I say it.
Two syllables, of course. Die-mund.
Three syllables, the ‘a’ is subtle, but it’s there.