And their falling out is all the more bitter because they were once so close.
The breakdown of such a significant partnership does not come without consequences, so where will it all end?
Mr Salmond believes he was the target of a "deliberate, malicious, prolonged and concerted effort" by people close to Ms Sturgeon to damage his reputation, even to the extent of having him jailed.
And when his two-week trial last year for sexual offences against nine women ended in his acquittal on all charges, it was clear he would seek revenge.
After refusing interviews and media appearances for the past 11 months, the former First Minister finally took the opportunity to speak out in a marathon six-hour session before the Scottish Parliament committee looking into the botched handling of the initial complaints against him.
In a calm but forceful performance – “more forensics than fireworks” as one TV report put it – he called for heads to roll, including those of Scotland’s top civil servant Leslie Evans, the Lord Advocate James Wolffe, and also SNP chief executive Peter Murrell, who is married to Nicola Sturgeon
He railed against Scotland’s “failed” leadership and even appeared to question whether the current government was fit to lead the country to independence.
And he talked about evidence he is banned from producing – text messages which he says show people "pressuring police", "collusion of witnesses" and "construction of evidence".
He stopped short of accusing Ms Sturgeon of being involved in a conspiracy against him, but said he had no doubt she had broken the ministerial code.
That’s normally seen as a resignation matter and there will be strong opposition demands for her to go if it is found she did breach the rules, but the convention of quitting for such behaviour was thrown into doubt when Boris Johnson refused to sack Home Secretary Priti Patel despite an independent report concluding she had broken the code by bullying staff.
Could the First Minister really be forced to quit in the midst of the Covid crisis and just weeks before an election?
Ms Sturgeon will give her version of events to the committee tomorrow. But her popularity ratings remain high – 86 per cent of SNP voters back her, with just seven per cent preferring Mr Salmond – and she is seen by the public as doing a good job in handling the pandemic.
Meanwhile, polls suggest the Salmond saga could affect the SNP’s chances of winning an overall majority at the elections, but the weakness of the opposition means there is little doubt about a Nationalist win.
It is support for independence which appears to be more at risk from the Salmond-Sturgeon fall-out, with the latest poll showing opinion now 50-50 (once don’t knows are excluded) after Yes leading for months.
After decades of fighting against the odds, it seems astonishing that, with the prospect of an independent Scotland looking closer than ever, someone who has devoted their life to achieving that goal is now willing to allow a bitter personal feud to endanger their dream.