ㅤㅤ𝑃𝑒𝑜𝑝𝑙𝑒 who fear being left were abandoned sometime in their earlier life— They'll assume one day or another you'll leave them even if you won't. They lack trust because the trust they had was taken advantage of.
ㅤㅤ𝓣 he best thing to do is to reassure them that you're not going anywhere. Your behavior and actions will be your proof. But if you show flakey behavior, dissappear without saying anything, walk away from yhem when they need you the most, mentally, they will put a wall around their heart and will have a hard letting you back in again.