1. To make sure you aren't imagining their actions or misidentifying the motivations for their behavior, notice their exact verbal and nonverbal behaviors, what they do and how often they do it, and in what circumstances they do it to see if it's consistent and triggered by interactions with you.
2. Have a conversation sharing what your partner did and how you felt about it. For example, "For the last three weeks, when we sit together at dinner, as soon as I start talking about my day or something I did or read, your turn and look away or touch or look at your phone." -State the concrete result. "I stopped talking." State how you feel. "I feel like your pulling away from me."