Indeed.
In one word - MIND.

Who tries to convince us that "we are meant to be together?" - The mind.
Who doesn't want to give up? The mind.
Who (often) produces illusions of attraction? The mind.

And what are those specific thought-patterns anyway? Just an aspect that hides behind those beliefs. The beautiful thing is that once you integrate that aspect, you free it, and allow an even grander love, more passionate partner, to come into your life. Not only that, thanks to the integration you even free the old partner to grow on their own way. It's a win-win situation although, at first in the midst of the drama, it doesn't look/feel like that.