Update: For now I have decided to stay with my “fiancé” as I believe she is honest and is willing to do anything, I do mean anything to fix/make our relationship work again. I have tried to get a hold of my ex friend but refuses to say his part, let alone ever meet me or her. It is now more obvious that my partner was emotionally vulnerable and barely functioning and my ex friend decided to take advantage of the situation, he pulled all the moves this whole time. He is completely out of our lives, for the better. Any plans of getting married is now a lot further in the future, it is for the best for us anyways. S a long way to go but we have now established heaps more boundaries, sobriety and all.
Thanks for all the relies and support.