This happen in the same time frame where Roland order that knight to raise chicken and ducks, he was going through the captive knights to give them their ultimatums.
Ferlin initially thanked Roland when he entered and swore fealty, Roland was surprised and asked for explanation.
In truth, Duke Ryan basically raped Irene when Ferlin was out on duty before.
Ferlin eventually found out one he returned and planned to kill the Duke during the skirmish, but Roland did that first.
When Roland gave him the choice of working in the mine or becoming a teacher, he chose teacher.
Later on Irene chose to migrate to Border Town, because considering the Duke raped her when Ferlin was a famous knight, now that he's a captive and no longer as the knight title, there's going to be more men coming after her.
She initially thought she'd have to live in rather shabby condition, the usual treatment for losing side.
Instead she was surprised to not only hear Ferlin was not treated like what is the 'normal' treatment for captives, but he's also got a job with his own units in a housing building.
Once she heard the detail of teacher job, she also applied to become one.