Who's Fault was it?

I just finished reading the Through the Moon book that was recommended when I asked about why Rayla left.

Before I read it, I always thought it was Callum's fault that their relationship was in a rocky place. I thought he was just being petty and he was upset over nothing. After reading it, I realised that Rayla betrayed Callum because she said they would go to Xadia together. This gave me the perspective that it was actually Rayla's fault.

I would have been very upset if the love of my life disappeared and all they left was a note which hinted at them never seeing eachother again.

Who's fault do you think it is?