Somebody who considers themself so tied to someone else that they are only there to do the other's bidding. A slave. By analogy with an actual third arm, with which the owner of the arm could hope to do so much more, but which has no independent life of its own.
Mary is trying to treat Jimmy like her third arm again. She won't even let him go out for a night with the lads.
churchhurt is where you experience a degree of distance, pain, or judgement from your church community. Essentially, you are just unable to “find your place”. This is prevalent in the Christian community, but can be extended to other religions.
Now that I am an adult I am beginning to heal from the churchhurt that was inflicted on me as a child.