I think that there are a lot of parts to abandonment.

Part is our perceptions: is the person abandoning us, or is that just our thought?

Part is the lack of control of others, their coming and going. Ackowledging that we have no control and coming to peaceful terms with it. We are all separate. Letting go of the false idea that we can control others is hard but relieving too.

Part of it is learning how we feel about being alone. It can be very frightening and there is much to learn about what frightens.

Looking at each part, and each piece of each part, in therapy might be helpful.