While reciprocal self-disclosure drives intimacy, digital tools seldom scaffold autonomy, competence, and relatedness -- the motivational underpinnings defined by Self-Determination Theory (SDT) that enable deep exchange. We introduce a chatbot employing dual-layer scaffolding to satisfy these needs: first providing enabling affordances (instrumental support) for vulnerability, then mediating affordances (relational support) for responsiveness. In a randomized study (N = 72; 36 couples) comparing Partner Support (PS: both layers), Direct Support (DS: enabling only), and Basic Prompt (BP: questions only), results reveal a critical distinction. While enabling affordances (PS, DS) were sufficient to deepen disclosure, only mediating affordances (PS) reliably elicited partner-provided need support and increased perceived closeness. Furthermore, controlled motivation decreased across conditions, and scaffolding buffered vitality, which remained stagnant in BP. We contribute empirical evidence that SDT-guided mediation fosters connection, offering a practical framework for designing AI-mediated conversations that support, rather than replace, human intimacy.

翻译：尽管互惠性自我表露是亲密关系发展的核心驱动力，现有数字工具却鲜少能同时支持自主性、能力感与关联性这三种由自我决定理论界定的、促进深度交流的动机基础。本研究引入一种采用双层脚手架设计的聊天机器人来满足这些需求：首先提供促成脆弱性表达的赋能可供性（工具性支持），继而提供促进回应的中介可供性（关系性支持）。通过一项随机对照实验（N=72；36对伴侣），比较伴侣支持（PS：双层）、直接支持（DS：仅赋能层）和基础提示（BP：仅提问）三种条件，结果揭示了关键差异：赋能可供性（PS、DS）足以深化自我表露，但唯有中介可供性（PS）能持续激发伴侣提供的需求支持并提升感知亲密感。此外，所有实验条件下受控动机均有所下降，而脚手架设计缓冲了活力感下降——在BP条件下活力感则停滞不变。本研究贡献了自我决定理论指导下的中介机制能促进人际联结的经验证据，并为设计“支持而非替代”人类亲密关系的人工智能中介对话提供了实用框架。