Athrun is given orders to kill Lacus and any on who may have helped her.
He also told that he must retrieve the Freedom because it is equipped with N-Jammer Cancellers and that technology cannot fall into the hands of the Earth Forces.
But Athrun is able to find Lacus at the first venue she ever performed at. They have a chat about what happened with Kira.
And some ZAFT people show up to kill Lacus, Athrun protects her and she escapes.
Athrun chooses to pilot the Justice (built alongside the Freedom) and goes back to Earth.
I think Lacus is really brave for choosing to stand up for what she and her father believe. She’s also brave for meeting Athrun and talking to him. Their romantic relationship may not have worked out but they still care about, respect, and trust the other. That’s an important relationship too.