Here is the situation, Nero is back in time, he can save Romulus, but also has advanced technology. In the film Nero talks to Pike on the Narada and states that not only will he save Romulus, but he will destroy the Federation so that she can be truly saves. This implies that either Nero has already informed Romulus of future events, OR plans to after the destruction of the Federation.
Here is how I see it though. Nero had a 25 year gap between destroying the Kelvin, and destroying Vulcan. In that time, what if he did go to Romulus? He literally shows up on their doorstep and says HI, LOOK WHAT I GOT! It's a perfect situation for the Romulans. Nero tells them about their impending doom, so that they can start making preparations for the Supernova. Nero then tells them about the plan to destroy the Feds. It's perfect for them. They have a supership, from another time, that can easily take out anything the Feds could throw at them. Nero seems like one who loves his home world. With this superweapon, he can attack and destroy all the Federation planets, and Romulus will have no responsiblity. He can act like a rouge, even though he may be been acting in league with the Romulan government the whole time. Yes, he told Pike he and the Romulans stand apart, but maybe he was lying. And if something happens, and Nero fails, the Romulans can sit back and say, we had nothing to do with it.
Here is how I see it though. Nero had a 25 year gap between destroying the Kelvin, and destroying Vulcan. In that time, what if he did go to Romulus? He literally shows up on their doorstep and says HI, LOOK WHAT I GOT! It's a perfect situation for the Romulans. Nero tells them about their impending doom, so that they can start making preparations for the Supernova. Nero then tells them about the plan to destroy the Feds. It's perfect for them. They have a supership, from another time, that can easily take out anything the Feds could throw at them. Nero seems like one who loves his home world. With this superweapon, he can attack and destroy all the Federation planets, and Romulus will have no responsiblity. He can act like a rouge, even though he may be been acting in league with the Romulan government the whole time. Yes, he told Pike he and the Romulans stand apart, but maybe he was lying. And if something happens, and Nero fails, the Romulans can sit back and say, we had nothing to do with it.