Görmeyince tükenseydi sevgiler,insan varlığı boyunca görmediği rabbine böylesi bir sevgi duyar miydi...

if love was to run out when not seeing each other would it not be the same for god that isnt seen throughout a persons existence 

I agree with the first sentence. For second one my try would be ;

insan varlığı boyunca görmediği rabbine böylesi bir sevgi duyar miydi...

would men since first existed, love to God this much that [although] he has never seen [God].

 Fine, it just sounds a bit "stiff" or "stilted" in English

Making it freer:

Could a man love God like this, whom he has never seen throughout his life?

(a) I changed would to could, as the sentence implies would he be able to

(b) the Turkish says "his Lord". We would more naturally use either "the Lord" or "God" here

(c) "throughout his existence" sounds really odd. "throughout his life" more natural.

(d) varlığı boyunca must relate to a man, not God, as God has no beginning and no end (ezelden beri, sonsuzluklar boyunca var olanı so I used a small letter for his, not a capital (we use capitals for God).

So the whole thing, in a free translation reads:

If true love were to fail when you don´t see the object of your love, could a man love God , whom he has never seen throughout his life?