Lean into this (as you may be projecting these beliefs onto your twin):
Where does the abandonment come from? Where was it established for you?
ie. it could have been from your parents, or family. where you were abandoned or felt like you were abandoned. it doesn't matter if they didn't actually abandon you or if you have a good relationship with them now. if you felt that way as a child or any reason, it matters and it was real for the child you at the time.
What to do with it now?
For abandonment, I recommend working through the trigger exercise as this allows you to acknowledge and recreate a new experience in regards to this.