George Kohlrieser is Professor of Leadership and Organizational Behavior at IMD. According to Kohlrieser,“a secure base is a person, place, goal or object that provides a sense of protection, gives a sense of comfort, and offers a source of energy and inspiration to explore, take risks and seek change".
In this talk we had some years ago, he offers his advice to people who have lost their secure bases.

What advice would you give to people who have lost their secure bases?
What they have to do is grieve, say goodbye and let it go. Because you can't say hello to a new secure base until you said goodbye to something. And then look around - what kind of secure base do you need - is it a person, is it a goal, is it a place? What can you use as a base to give you that foundation of inspiration inside, in order to be able to be successful?
Secure bases are fundamental for success. We have to go trough a series of those in our life generally. And what happens is you need a network of them.
So saying goodbye.
Finding a new secure base requires curiosity - what is around me, what do I need and how do I start looking for those things that make me feel secure and successful.

Part of our talk with George Kohlrieser on Why you could be a hostage without a weapon, You could read here