Did Cupid Made a Mistake or is it Because of Fate

Cupid is the ancient Roman deity of love in all it's form, we also know when cupid strikes with his golden bolts, one could be hopelessly in love.
But why can't people love the ones who love them genuinely instead of the ones who can't love them.
Why are there people who have been single for a long time?
Why is it that a perfect relationship ends?
Is this a hint that cupid made a mistake or is it the result of fate?