Does he find his cousin attractive?

My boyfriend and I visited his cousins for Christmas. They live in the US and my boyfriend and I live in Canada. Therefore he doesn’t see them much. One is a boy same age as us, the girl is 2 years old. Today we went out and I realized he is VERY talkative to her and ONLY her. She has a boyfriend but every time the boyfriend talks or the boy cousin talks he is VERY short off and wouldn’t even try to make conversation. When the girl talks he leans towards her and turns his body away from me more towards her. Her boyfriend was acknowledging her and putting his arms around her. Mine literally acted like I wasn’t even there. Ever time he would ask a question like “should we get more to eat” he looks straight at her and only her before she even says anything. I know he doesn’t see them much but he was only like this with the girl. The second he dropped them off he started acting like normal, and acted like I was there.
Is this overthinking, or is there something?
Does he find his cousin attractive?
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