In my opinion - mind you, my opinion only (: - this is one of the defining moments for Aliena. After her rape, even though she battled much, she never felt like herself again. In one way, she cowered - as the quote puts it, she was a cocoon. Aliena was this shining beautiful girl, and she got reduced to a shell. And by loving Jack - and mostly, Jack loving her back - she got back to herself, somehow.
I think this quote says a lot more about Aliena than about the relationship between her and Jack - not that she really needs Jack or depends on his existence, but she loves him because he reminds her of who she was before. By loving him, Aliena could finally allow herself to love who she was, to find out her strenghs again, and accept who she is. She can remember that she’s not entirely broken, but has something to fight for, and people who believe in her. Once again - she was a living shell, and after this she has become a person again.
Hope this helps (:
Indira Varma as Mattie Wise in World Without End (2012).