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Jonathan and David had a very close relation. They were the best of friends, who trusted each other in very trying times with Jonathan's father, King Saul. They had a brotherly love for each other, and desired to see God's will be done in the Kingdom of Israel.
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The relationship described in 1 and 2 Samuel between David and Jonathan was touchingly close. The description of Jonathan's love for David, in 1 Samuel 18:1: "And it came to pass, when he had made an end of speaking unto Saul, that the soul of Jonathan was knit with the soul of David, and Jonathan loved him as his own soul," is of either a close brotherly bond or of something much more erotic. When David speaks of his love for Jonathan in 2 Samuel 1:26: "I am distressed for thee my brother Jonathan: very pleasant hast thou been unto me; thy love to me was wonderful, passing the love of women," he does so in terms appropriate for a close homosexual relationship, even while calling him as "my brother Jonathan."
King Saul confirms the nature of their relationship in 1 Samuel 20:30 : "Then Saul's anger was kindled against Jonathan, and he said unto him, Thou son of the perverse rebellious woman, do not I know that thou hast chosen the son of Jesse to thine own confusion, and unto the confusion of thy mother's nakedness?" There could have been other reasons for Saul's anger at just this point in time, but 'confusion' ( or 'shame') has sometimes been used as a euphemism for forbidden practices; this combined with the reference to his mother's nakedness
On the biblical evidence, it appears the relationship between Jonathan and the future King David was one of homoerotic attraction, even if there is no direct evidence of physical consummation.