Cyrus, 19, and the 22-year-old Australian hunk began dating in 2009 after falling in love on the set of their romantic drama The Last Song and, in June (12), they became engaged.
But the former Hannah Montana star admits things were not always great between them and they secretly split once or twice - so she could act out her teenage years before settling down.
She tells Marie Claire magazine, "Liam and I have a really good relationship. It took breaking up once or twice because I was young and immature and wanted to do things I hadn't yet gotten to do.
"He was older, so it was like he'd already been through school. At some point you realise these people you're hanging out with are your 'party friends'; they're not going to give a s**t about you in 10 years. Then you remember who you really want around you."