This is exactly what they do. They tell themselves the whole mess they are in is all your fault because you can't possibly be what they need you to be. This 'fact' therefore makes it a logical decision to part ways, which of course then the whole world must assume makes it mutual, right? <eye roll> Trust me - I've heard this one before.
My XH was very taken aback when I refused to pay any of the legal costs on the grounds that our divorce was absolutely, entirely, 100% his decision. I even told him "had the decision been mutual I'd have been happy to foot half the legal bill". Needless to say, he still hasn't responded to that one.