I'm actually impressed with kai for not telling Olivia his reasons. I'm pretty sure he went into casa happy enough with her but it was the boys and the other girls who questioned her intentions with him and made him realise she had jumped from multiple men and was still obsessed with tom. He wasnt going to throw other people under the bus and have them have to deal with her drama too.
In casa he realised he got on with Sanam and liked her more than Olivia and was genuinely happy for Olivia that she found someone too. He probably would have been more than happy to be friends until she stood at that firepit and tore him apart like he meant nothing to her. She is the one who implied she had doubts about him going into casa saying she wasnt surprised and isn't shocked he recoupled instead of saying we did have a connection and I was happy going into casa but I felt I got on better with max and I'm glad to see Kai has also found someone he connected with more. But no she was absolutely raging he was happy she wanted him to be single and pine after her.