The former Dancing with the Stars contestant, who has three children with Australian Football League player Brendan, said that she will always "care" about him but could not stay with him after his gambling, drinking and cheating scandals.
Alex told Sunday Night: "It's not just the gambling or the drinking or the cheating - it was just the whole thing. I couldn't see how I could possibly trust him again.
"I will always care about Brendan. He is the father of my children and he is a great person in a lot of ways, [but] he's just got a lot of problems. He has made a lot of bad decisions and needs to do a lot of growing up."
Alex added: "It's very difficult to come to the decision to actually say, 'That's it, I've had enough'. When you get married, you assume it's for life."
Earlier this year, Brendan admitted that he had attempted to commit suicide after a fight with Alex. He recently spent time in a rehabilitation clinic after a much-publicised battle with alcohol.
Alex left Brendan last June shortly after he publicly admitted to a gambling addiction.
He was also axed from a TV advert after his alleged involvement in the leaking of former lover Lara Bingle's nude photograph in 2010.