How do you get a friend back after they have made a new friend?

First of all, any person can have more than one friend, and often do. Don't automatically think that the appearance of a new person means that you no longer matter. Sometimes two friends cling together during a particularly rough time, and when things ease up for one of them, they feel more able to spread their wings and talk with more people. Try not to see this as a threat. You may have to make adjustments, but that is okay. Be sure to tell your friend in a non-demanding way how important they are to you, and that you want to set up a time to get together if you haven't seen them in a while.