Not everyone is meant to come with you to the next chapter. Thank them for the one they were in.

Friendships are often held together by a shared situation rather than by a decision, and when the situation ends some of them quietly end with it. The same bus, the same team, the same class was the thing in common, and that is not small while it lasts. Losing touch is not always a failure or a betrayal. Some people were genuinely right for one specific stretch.

If somebody is drifting out of your life, let it happen gently and say the true thing first. Thank them for the part they were in. No argument required.