As your setting changes, the people in your social circle will change as well. The revolving door of acquaintances and friends is natural, though there are some who should never leave your acquaintance. Few of your friends now are worth speaking to later, and of those, few will ever have the initiative to reach out to you rather than the other way around.
If you still want to be around certain people, take responsibility for the task and try to speak to them. Don’t mistake their inaction for rejection. Make it your pleasure to maintain relationships even when it’s difficult.