Life, Relationship change
Tetsu just couldn't take it anymore, and they finally broke up.
Kale didn't cheat once, but twice on Tetsu. Kale didn't have a good grasp on how a relationship should be due to his past trauma, and wasn't ready for things with Tetsu. Kale understands that he hurt Tetsu, and he feels horrible about it. After Tetsu has time to overcome the heartache, they are slowly able to become friends, since Tetsu understands about Kale's struggles.