In the 2019 book "Lost Connections" by Johann Hari, he states that loneliness creates both anxiety and depression. Loneliness does not mean being physically alone, it means not been connected to another person in a meaningful way.
In the CPT [see chart] it means connecting Self with Others, based on Hope and achieving Oneness of purpose. To turn hope and oneness into joy, there also needs to be a balance between Principles [Trust, Respect, Acceptance & Commitment] and Comparative Thinking [How are we going towards this goal? Are we succeeding or failing?]
-Your Trust, Respect, Accept and Commit to them and they to you. AND
-You Trust and Respect yourself, that you have the knowledge, skill and experience to add value to the relationship AND to accept and commit to the common goal.