And tarried in a place - He probably waited till he saw all his friends safely out of the city.

Cherethites

2 Samuel 8:18 And Benaiah the son of Jehoiada was over both the Cherethites and the Pelethites; and David's sons were chief rulers.

2 Samuel 20:7,23 And there went out after him Joab's men, and the Cherethites, and the Pelethites, and all the mighty men...

1 Samuel 30:14 We made an invasion on the south of the Cherethites, and on the coast which belongs to Judah, and on the south of Caleb...

1 Kings 1:38 So Zadok the priest, and Nathan the prophet, and Benaiah the son of Jehoiada, and the Cherethites, and the Pelethites, went down...

1 Chronicles 18:17 And Benaiah the son of Jehoiada was over the Cherethites and the Pelethites; and the sons of David were chief about the king.

gittites

2 Samuel 15:19-22 Then said the king to Ittai the Gittite, Why go you also with us? return to your place, and abide with the king: for you are a stranger...

2 Samuel 6:10 So David would not remove the ark of the LORD to him into the city of David...

2 Samuel 18:2 And David sent forth a third part of the people under the hand of Joab, and a third part under the hand of Abishai the son of Zeruiah...

1 Samuel 27:3 And David dwelled with Achish at Gath, he and his men, every man with his household, even David with his two wives...

Loyal to the Core
On the other hand, look at Ittai, perfectly free to go, but in order to end the controversy once for all, and to make David know that he does not mean to leave him, he takes a solemn oath before Jehovah his God, and he doubles it by swearing by the life of David that he will never leave him; in life, in death, he will be with him. He has cast in his lot with him for better and for worse, and he means to be faithful to the end. Old Master Trapp says, "All faithful friends went on a pilgrimage years …
Charles Haddon Spurgeon—Spurgeon's Sermons Volume 26: 1880

Samuel
Alike from the literary and the historical point of view, the book[1] of Samuel stands midway between the book of Judges and the book of Kings. As we have already seen, the Deuteronomic book of Judges in all probability ran into Samuel and ended in ch. xii.; while the story of David, begun in Samuel, embraces the first two chapters of the first book of Kings. The book of Samuel is not very happily named, as much of it is devoted to Saul and the greater part to David; yet it is not altogether inappropriate, …
John Edgar McFadyen—Introduction to the Old Testament