People come and go from our lives all the time, some sooner and some later, the main thing to focus on is not trying to get them to stay longer, but enjoying the time you have with them. If your friendships don’t last it is just nature telling you it is time for a new friend. You cannot expect to find everything you are looking for in one close friend or relationship. It doesn’t mean you have to say goodbye to that person, it just means you need to open yourself to something more and new. Try not to spend all of your time with just a few select people, instead spend smaller amounts of time with many different people.