This rhetorical question emphasizes David did not want Ittai to come. This question can be translated as a statement. Alternate translation: "I do not want to cause you to wander around with us." (See: [[rc://en/ta/man/translate/figs-rquestion]])
Here "yesterday" is an exaggeration that emphasizes a short amount of time. Ittai the Gittite had lived there for several years. Alternate translation: "Since you have lived here only a short time" (See: [[rc://en/ta/man/translate/figs-hyperbole]])
This is a blessing that David is giving to him. Alternate translation: "May Yahweh be faithful and loyal to you always" (See: [[rc://en/ta/man/translate/figs-explicit]])