So, it makes sense in that expression; " God requites the charitable" would mean God gives back to those who give to others, which is certainly a nice idea.
By preventing us from properly growing close to them, the beloved also prevents us from tiring of them in the cathartic and liberating manner that is the gift of requited love.
When you have unrequited love, or perhaps you had " requited" love – someone loved you and then left you – you just have to think of the great Gloria Gaynor and her song " I Will Survive."