Albert Barnes Commentary 1 Samuel 18:8

"And Saul was very wroth, and this saying displeased him; and he said, They have ascribed unto David ten thousands, and to me they have ascribed but thousands: and what can he have more but the kingdom?" — 1 Samuel 18:8 (ASV)

What can he have ... Rather, “There is only the kingdom left for him.” For the same sentiment, compare 1 Kings 2:22. As Camden says, “A kingdom tolerates no companion, and majesty more heavily takes injuries to heart.”