"W-Why? What makes you reluctant?"
Bella looked Tristan in the eye and said, "Tristan, I've promised someone..." Her voice trailed off when she saw his worried gaze.
She can't bring herself to tell him that she promised Sean Spencer a chance—if Sean's parents one day accept their relationship, she'll give him a chance, try to love him, and marry him. This made her reluctant to decide, as she had to meet Sean to talk heart-to-heart about this matter.
If she accepted Tristan without meeting Sean, it would betray her promise to him. The thought of hurting Sean or breaking the trust they had built was unbearable.
Tristan felt his heart slowly ache as he guessed what was bothering Bella at the moment. He didn't want to put any pressure on her or put her in the corner, so he promised to wait until she felt ready to tell him.