This is an ambiguous question.
1. How many exes can one have?
You could have as many exes as you've broken up with.
For some reason there is only one whom you keep going back to.
In essence there is only one ex and a hundred other forgotten exes
2. Ex is used before words to indicate previous
how many ex servicemen live in wansbeck northumberland uk
The 2012 Infiniti EX has 24 valves.
The 2011 Infiniti EX has 24 valves.
The 2013 Infiniti EX has 24 valves.
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5 ex-am-i-na-tion
He is your ex-husband. Many people just say my "ex".
There are 3 syllables. Ex-cit-ed.
There are 3 syllables. Ex-plor-ing.
There are five syllables. Ex-as-per-at-ing.