Or is it a what? We most often see that story played out in movies and books and TV shows where someone is interested in power or money or prestige and so attempts to or successfully enters into a relationship with someone who can give them that. The story can be a morality play showing the evils of greed or too much desire or it can be more open ended showing the results for both parties and not making any judgements. So the thing that the person is in love with is not the particular person they make the object of their affections, but the role they are acting out. Which can be just fine if the other party knows and agrees to that. Centuries of arranged marriages have been based on this and been successful. Have they been romantic triumphs? On average no, but that was not the stated goal so no harm no foul.
But what happens if the object doesn’t know that they are desired for their role and not for themselves? Well, Shakespeare’s comedy’s enjoy using this as a means to make us laugh, making sure that everything works out well in the end. The morality tales use this to show that it never works out well for anyone. And soap operas are based on this. It’s the basic plot on which all the details rest. You did THIS because you wanted THIS and not ME. *close up…fade to black* I’m fairly sure that all of us can find examples of us being the object in a situation like this and, if we’re honest, being the person who does this.
And then there is the really difficult situation of not knowing that this is what you are doing. Mistaking the role for the person. Wanting a relationship so badly, wanting it so strongly that you invest everything you have into getting it and holding onto it. Making the relationship your identity. Then having it end. Because at the ending, like the aftermath of a train wreck, as the shock wears off and the reality starts to come into focus, 
all around will be bits and pieces of things. And in sorting and sifting and trying to put things together, the pieces will not fit. Because they aren’t what you thought they were. The relationship wasn’t what you thought it was. It wasn’t a role you were in relationship, it was a person. And that person wasn’t the role they were in, they were much, so much more than that. And what they wanted and what they needed only matched up with the role for a certain amount of time. And then it didn’t any more. And because you were in relationship with the role, they didn’t want to stay in relationship with you any more. Sifting through the wreckage will show evidence of who they actually were, which can be a revelation.
The bigger revelation will come if and when you realize that it wasn’t a who that you were in love with, but a what.