Yes, it is all your fault!

I have personal experience in both receiving and giving the line "It's not your fault" in a breakup of close friendships and close relationships.  I just want to say for anyone out there, this line is incredibly frustrating and you should never use it.

Reason being, in order to come to terms with the end you need resolution - closure.  "It's not your fault" leaves the person who delivers this line absolving the recipient of all guilt and all responsibility - but this is a bad thing, for without guilt or any degree of responsibility there is nothing the recipient can take and resolve.  The effect of this line is to cause the recipient to be left without closure.  They will in their own minds insist that it was something they did, no matter how hard you persist in your words this thought process cannot be escaped it will happen.

Absolving the person of guilt or responsibility will leave them in a prolonged state of confusion and upset.  Now if you had said the counter, that it was indeed their fault, all their fault then they would have the necessary to rebuke your accusations.  If the accusations are in earnest then they can take constructive criticism away with them and develop further.  If the accusations are not in earnest or if the recipient thinks they are unfounded or unfair then they will argue with you - this is good, arguing is healthy it is how we vent out the emotions that if  bottled up would cause us to become prisoners to our thoughts and feelings.

You have to do what is best, and despite what we are lead to believe the route of avoiding confrontation at all costs is not the healthiest route to progress down.  If you want the other person to move on, if you want them to be able to let you go then you have to give them that chance.  "It's not your fault" as noble as these four words are they can do more harm than good.

We only argue with people whose opinions we actually care about.  Otherwise the argument is pointless.