Mr Oyinlola served as governor in Osun between 2003 and 2010 under the umbrella of Peoples Democratic Party (PDP). He later defected to the All Progressives Congress (APC) shortly before the 2014 governorship election in the state.
He was one of those who campaigned for Mr Buhari ahead of the 2015 general elections.
Speaking on BBC Yoruba programme on Thursday, Mr Oyinlola said those that supported and canvassed for Mr Buhari are already seeking forgiveness from God.
The BBC interview was monitored by our correspondent.
“I participated in the process that brought in Buhari as president. We made several promises to Nigerians but we are yet to fulfill any. One of many cases is security. We thought because he (Buhari) was a former military head, he was going to eradicate Boko Haram in six months but nothing has changed.
“Obasanjo told us that he knows Buhari, and not sure he could lead Nigeria well, but we felt because he is a former military head, he should be able to tackle insurgence. Since we gained independence, and civil war, there’s no moment more scaring like what we have now.
“The newspaper reports we read daily capture death and abduction of people. Already, parents are not interested in sending their kids to school. Insecurity has not gone worst like this since 1999,” the ex-governor said.
Mr Oyinlola, who has returned to the PDP, also advocated for restructuring, saying Mr Buhari is acting ignorantly about all he promised in 2015.
“I am surprised that we have not seen a difference. We promised the southerners restructuring but I am surprised that Buhari is acting so ignorantly about restructuring now. We lobbied them with restructuring promises. We are seeking forgiveness from God over these matters.”
He also advocated for the dissolution of power to states.
Nigeria has been battling various forms of insecurity in the last few years. One of the many security challenges is the crisis between farmers and herders across various parts of Nigeria.
The 17 southern governors in Nigeria, on May 11, resolved to ban open grazing of cattle in their states. The governors said the incursion of armed herders, criminals, and bandits into the Southern part of the country has presented a severe security challenge such that citizens are unable to live their normal lives.
Many groups are also calling for restructuring but Mr Buhari has refused to take any step on that. His refusal has led to Biafra agitation in the Southeast and Yoruba Nation agitation in the Southwest.
However, an ex-Governor of Lagos, Bola Ahmed Tinubu, alongside the Speaker of the House of Representatives, Femi Gbajabiamila, Bisi Akande and all leaders of the All Progressives Congress (APC) in the South-West, in a meeting in Lagos last month, strongly opposed the agitations.
They called for ethnic and religious unity, instead of a divided nation.