The person with whom you used to have casual sex, but now you don't want that no more

Someone who shares your pain. Someone you can always call, day or night, when you can't take it anymore, because he/she knows exactly what your going through. Someone with the same condition (mental/ physical or chronic illness) or experience as you. Someone you can relate to.
(Term created by Ruby Wax // From the book: Sane New World.)