Shame and guilt

Regret coiled around Julian's shoulders like a heavy serpent, squeezing the air from his lungs. The sting of realization pierced through him, a bitter reminder of all the warnings he had chosen to ignore.

Esme had tried to warn him several times about Ruby's deceitful nature. She and his father had told him how manipulative Ruby was, but he had turned a blind eye to their concerns. 

The ache of regret gnawed at him. Julian got the startling sense that all of his energy had been drained. He couldn't believe that his attraction toward Ruby had blinded him to the point where he had wounded his childhood friend- his only good friend since he was a child.