According to a source, Liam and Miley needed to do some growing separately. As a result of their separation, they are now in a more mature and really healthy relationship.
Liam is also much more vulnerable and vocal with his feelings, which is what Miley wants all along. So the breakup did serve them both well.
They just needed the time to figure out what they really want. And now both Liam and Miley already know what they want so it is likely that their relationship would go the distance this time around and perhaps a walk down the aisle is no longer remote at this point in time.
Contrary to rumors, Liam actually never gave up on Miley just when everyone thought that he has moved on.
While Miley went on to come out with chart-topping music after they split and also did some serious personal causes, Liam realized that she was merely growing up and experimenting. So he took a step back and gave her time to do whatever she wants.
But all those time, she never gave up on Miley and the good thing is that they never stopped loving one another. Now that they are officially back, it looks like there will be more things in store for the two of them in their respective careers and their relationship too.