Jakeb had a dream his ex got with his brother's best friend. He didn't feel bad or have any remorse, he knew what his brother's friend was about.
He was a player and nothing serious would become of what was going on. She tried to make him jealous because she thought it would give her the upper hand. He knew anyone after would be a downgrade.
He felt nothing because her games made him become emotionless. She violated his trust and wasted his time her opinions no longer mattered. He went numb when it came to her. She couldn't change or manipulate him anymore.