This may be heavily subjective, but "FWB" situations in which both parties are attracted to the other's body and mind are unrealistic... or at least unsustainable (in my eyes). If I were your INTJ friend and began to develop feelings for you it would cause intense emotional distress toeing the Friendship line you drew in the sand. I would wonder why you drew it in the first place--which of my qualities made a relationship unappealing? It sounds like lack of communication fueled most of your issues together... I hope you find the heart-to-heart you're looking for.