Why did he say "Gam Ish Shlomi
Radak: The Choleh says, every person has haters. When he gets sick, even those whom he thought were lovers, they become enemies and ambushers - "Kol Achei Rash Sene'uhu" (Mishlei 19:7).
Why did he say "Ochel Lachmi"?
Radak: Even one whom I feed, that I trust in him more [betrays me].
Malbim: Even though I was careful to take food only from my faithful servant, whom I trusted not to do evil to me, also he ambushed me and plotted to put poison in my food. He is called Ochel Lachmi, for the custom of early kings was that the one who serves food to the king, first he must eat some, so it will be known that there is nothing bad inside. Even so, he plotted with them, and did not fear lest he need to eat first 1 .
If normally David told him to eat first, this is like suicide! If normally he did not eat first, why should he fear? Perhaps David asked him to eat very rarely. Or, he always ate a small amount, which would probably not kill him. Or, normally he did not eat, but now that David sensed a plot, David might tell him to eat. (PF)
What is "Higdil Alai Akev"?
Rashi: He ambushes. This is like "v'Es Akevo mi'Yam la'Ir" (Yehoshua 8:13).
Radak: It is as if I am the tread mat on which he steps - so he aggrandizes himself over me, and does not visit me properly.