The William Woodside in the 1918 marriage is a bachelor. So either it is a different William Woodside to the one who married in 1900, or if it is the same man perhaps he lied to conceal a bigamous marriage?
There were 3 William Woodsides aged around 22/23 in the 1901 census so I wouldn’t rule out the possibility it’s a different William.
Likewise the 1911 census William in Cork is a bachelor. So may not be the right man. (Though his age, county of birth, denomination and occupation do seem right).
Abraham Woodside died 7.3.1902 Belfast.