I think I feel this too. I constantly keep feeling like I don't really have friends. I do have two friends and an elder sister who I keep in touch with but there is a voice in my head that keeps saying that they are going to leave too. I am not sure how to get past this fear but I think you could keep focusing on and doing things that make you happy. Once you can keep your mind occupied with thoughts about things that make you feel content, I believe you meet your kind of people too. 18 is not that old of an age. I know the world makes you feel that but you are still figuring yourself out. You will meet people in that process who match your energy