Australian pop singer Jessica said the Smashing Pumpkins singer has gone from ''boyfriend'' to just ''friend'' status after two years together.
She added to Australia's Daily Telegraph newspaper: ''It's one of those things. It's really difficult when you spend so much time apart.''
Jessica is thought to be the inspiration behind The Smashing Pumpkins latest album, 'Oceana', while Billy contributed to the new Veronicas LP 'Life on Mars'.
After fans of The Smashing Pumpkins took to twitter to criticise Jessica, Billy leapt to her defence, tweeting: ''It seems some among you have construed that there is an issue between me and my ex @Jessicaeronica, some hidden thing.
''I'm taking to Twitter (because I see where she is being attacked here) and I ask that she be respected as a woman I love and admire. Although our relationship has ended, we remain the best of friends and I ask that if you respect me you'll treat her with the same respect. (sic)''
Jessica responded to one nasty comment by writing: ''This is real life. Not some accessory for you to play with and twist around. You know nothing.''
When asked by Australia's Triple M radio if he was ready to marry he said: ''Listen, you gotta take it up with the twins... When you have a relationship with the twin, you have to deal with the other twin and then you've got to deal with the twin you're with.
''The funny thing is they're both such different people but kind of ... One mind. But you kind of get The Feeling they wouldn't hesitate to kill you if you got in their way.''