I think it's more of he's obsessed/smitten with Yeonwoo & would do anything for him given the opportunity. But also is trying hard to hold back & not overwhelm him, considering his past trauma. I think Yeonwoo will be the only one to get the puppy side of Kim Shin, cause homeboy definitely is NOT the slightest bit submissive or eager to cater to to anyone else besides Yeonwoo.