He did that cause of what the alpha said that worsen his insecurities. He want to check if it's really true and he can't use his fingers since he won't know the difference so he decided to use the other alpha's hand and experience if it's really true.
(Da** didn't know people consider dropping it just because of him having other alpha check his whole when they managed to not drop it when he got sa and become s t. But it's their own choice)