I understand that one can talk to their fiancé provided there are no lustful intentions. Is this correct? If so, is saying words such as 'I love you' allowed?
No, it is not allowed to tell your fiance: I love you, simply because there is no religious frame (Aqd) between you like Nikah or Mut'ah. Your fiance remains non Mahram to you until you have such Aqd recited between you with its conditions like the permission of the father of virgin girl.
Wassalam.