As marriage proposals take place between elders, even Kaikeyi might also be ignorant of this arrangement.Dasaratha was optimistic that as mANDHARA HAD JOINED Kaikeyi after her martriage she too would have been ignorant of this Rajya sulkam.
Dasaratha was crazy about Rama. So he was desperate to overlook his promise to Kaikeyi.But in this issue Fate has helped Dasaratha in not becoming asatyavan.
The reason for Dasaratha for going to Kaikeyi s abode was mainly to convince her in this major issue. He was confident that she liked and loved Rama very much.So even if Bharatha came and questioned him regarding this injustice he could easily say that as his mothe ralso did not have any objection , he proceded wihth the idea.
Overall Dasaratha was suffering from guilty conscience.He knew he was doing wrong.He was caught in web of immnse love towards Rama.He was ready to overlook his promise and godown as asatyavan in the panels of history.