Yago Riedijk and Ms Begum married shortly after she arrived inside ISIS territory in Syria.
Speaking to the BBC, he confessed to fighting for the group but says he now wants to return home with his spouse and their newborn baby son.
Mr Riedijk, 27, is currently being held in a Kurdish detention centre in north-eastern Syria.
He faces a six-year jail sentence for joining a proscribed terrorist organisation if he returns to the Netherlands.
Mr Riedijk told the BBC that he now rejects ISIS and did try to leave the group.
He told the BBC correspondent that he was detained in Raqqa and tortured by ISIS after group accused him of being a spy for the Dutch authorities.
Ms Begum, who is now 19, fled with Mr Riedjik from the town of Baghouz, ISIS’s last territory in eastern Syria, as the so-called caliphate disintegrated.
The Dutchman surrendered to a group of Syrian fighters, and Ms Begum and their newborn son, Jarrah, were placed among 39,000 people in the al-Hawl refugee camp in northern Syria.
Ms Begum has reportedly gone elsewhere due to personal safety.
She left Britain in February 2015 with Kadiza Sultana, who was 16, and Amira Abase, who was also 15 at the time. Ms Sultana is believed to have been killed in an airstrike in 2016.
The Home Office has revoked Ms Begum’s UK citizenship on the grounds that she is a Bangladeshi national through her mother, who holds a Bangladeshi passport.
But Bangladesh’s ministry of foreign affairs rejected this, stating that Ms Begum is not a Bangladeshi citizen and that she will not be allowed to enter the country.
Last month, Ms Begum’s family told Home Secretary Sajid Javid that they were going to challenge his decision to revoke her British citizenship.
Labour leader Jeremy Corbyn, said Ms Begum has a “right to return to Britain” – and described the decision to revoke her citizenship “extreme”.
Mr Riedijk was born and raised in the Netherlands but abandoned left his life in 2014 to join ISIS.
He was among 300 Dutch men and women who travelled to Iraq and Syria and Iraq.
Of those, around 135 Dutch nationals with “jihadist intentions” are still there, anti-terrorism officials have said.
Mr Riedijk has not had his Dutch citizenship revoked, although he is on a terror watch list.