After sending the message, Liam did not look back and continued walking forward. He was fully aware of what he had done, and he did not plan on being anywhere in the vicinity when the shit hits the fan.
As for why he had done it, he simply had no other choice. It was not as if he was fond of backstabbing in this way. He would rather be straightforward and brutal. But he had already considered this from several perspectives, and if he tried to keep his word, the only outcome he was able to see was his death.
This mysterious being was a prisoner, imprisoned by possibly one of the most powerful factions in this world. What would happen if word spread around that he helped the person escape?
Even if the divine temple let this matter rest, would the prisoner let him live? He was the only one alive who knew that she had escaped or was at least close to escaping. Wouldn't she want to erase his existence to remove all evidence?