1.) You can romance an intelligent weapon 2.) A slime monster has become intelligent. It can change into almost any form (animal or humanoid), but it remains very slimey. 3.) One of your companions turns out to be a shapeshifter. 3a) It is a monster which disguises as humonoid to attack humanoids. It is dating you to be alone with you and eat you then. (option1: It is random which one is the monster. option2: Its a succubus) You can still convince it to stay in your party and romance it. 3b) It is a very ugly human of the opposite sex than the one it seems to be. 3c) I will vote for kitsune race in the new pathfinder game. You can romance a fox.
I am also planning on getting Pathfinder Wrath of the Righteous but I am not keen on the new animal races there are going to put in by poll so I will be giving the poll a pass but on the other stuff I have seen a story on youtube that goes on the lines of what you have said
D&D Story: Seducing Monstrosities - 1
D&D Story: Seducing Monstrosities - 2
Cthulhu: FOR THOUSANDS OF YEARS I LAY DORMANT, WHO HAS DISTURBED MY- Oh its you... Warlock: Greetings my lord- Cthulhu: LET ME SLEEP-