John Gill Commentary 1 Samuel 20:9

"And Jonathan said, Far be it from thee; for if I should at all know that evil were determined by my father to come upon thee, then would not I tell it thee?" — 1 Samuel 20:9 (ASV)

And Jonathan said, far be it from you To entertain such a thought of me, or to have the least suspicion of me, that I should conceal my father's ill intentions against you, if known to me;

for if I knew certainly that evil were determined by my father to come upon you, then would I not tell it you ? certainly I would; can you doubt of my kindness and fidelity? surely you have no reason, when such a covenant of friendship subsists between us, and there has not been the least breach of it on either side.