The question I have is whether either one has truly "lost faith". I am a cynic in this case and believe that a lot is both financial and agent/adviser driven.
If Fabregas' desire to play for Barcelona was truly emotional homesickness based, he would put in a transfer request and put an end to our misery. No one would begrudge him the desire and many would applaud his conviction. As he has not put in the request which would cost him 2 or 3 million - he loses the signing fee that is payable to him - suggests that this is driven by money. He knows that he will spend more time on the bench than starting for the next 3 or 3 years. It is easy money for him.
With regard to Nasri, he has just come off a a career half-season. I suspect that his advisers have said that Fabregas is going and that he is going to have to carry the team during a very tough transition season. He is looking to cash in on the "reputation" before the possible Arsenal demise drags his value down.