Oh Simon, it just isn't fair, is it? I, too, have been there. I was played for many years. Guess I was stupid or a slow learner. I did learn, however, and I finally cut this person out of my life for almost five years.
Well, this person realized what they were missing with me out of there life and this year, finally apologized for all those years. I accepted the apology but I will never trust this person again or let this person get close to my thoughts again, although they keep trying. So, what I am trying to say is, eventually, these people WILL realize what a true friend they had in you and they will be sorry.
Good luck to you and I'm sorry this is happening to you.
Linda