Stage 1: NT meets NF. NF is enamoured of NT, falls head over heels. NT is characteristically cautious, but interested. NFs are fun, after all.
Stage 2: NF appreciates and admires many characteristics of the NT and thus begins to behave more like an NT, perhaps even fooling the NT into thinking s/he is an NT. NT then relaxes, figuring s/he's with a kindred spirit, gets more comfortable with the relationship, starts acting like normal NT self, expecting to be understood.
Stage 3: NF feels NT cooling off and wonders what s/he is doing wrong. Tries to be more like NT to compensate. This doesn't feel right. NF gets needy and/or begins to consider is her/his duty to draw the NT out of her/his shell, encouraging the NT to express all those feelings buried deep inside. NT doesn't get it.
Stage 4: NT feels pressure from NFs emotional demands, needs distance to figure things out. (This might be only INTs. I'm not sure.) NF panics, becomes more needy. NT withdraws more...NF needs more...and so on and so on.
Stage 5: NF suddenly realizes that the reason things aren't working is that the NT is cold and unfeeling or not nurturing or some other horrible thing. Abandons NT without looking back. (This is especially likely with the NFPs.) NT is confused and (sometimes) relieved.