1 Samuel 18:21-22, 29

Saul thought, “I will give her to him that she may become a snare to him, and that the hand of the Philistines may be against him.” Therefore Saul said to David, “For a second time you may be my son-in-law today.” Then Saul commanded his servants, “Speak to David secretly, saying, ‘Behold, the king delights in you, and all his servants love you; now therefore, become the king’s son-in-law.’ ”

then Saul was even more afraid of David. Thus Saul was David’s enemy continually.