My adult stepson..
I got married to my wife when my stepson was 12 year old. He didn't seem to care that his mom was marrying another woman. However he kept his distance. He rarely said hi or hello to me at home. Soon that behavior bled into the way he treated his mom. He clearly preferred to be at his dad's place. He is a 27 year old phd student in biophyiscs/ biochemistry. When ever he gets free time he always visits his dad. He only sees his mom once a year and he is only one state away, yet he has been at his dad's place four times yearly. Last Thursday was my wife's birthday. He couldn't even facetime her for at least 20 minutes if not visit. He just said happy birthday for five minutes and told us he was busy with his friends on a trip. My wife's mood was soured for the entire day. I got really upset and personally called him to have a meeting for three of us. He reluctantly said ok after saying it was urgent.
We met at the cafe nearby his university. I basically told him how I felt the way he treats his mother for all these years. His expression was stone cold. He told me I was being unreasonable. He openly admitted he loves his dad way more than his mother. My stepson said the moment I entered into the family, was the moment he felt sidelined. He seemed upset at the fact whenever he asked to do stuff with just his mother, she would always suggested me to tag along or would have made plans with me before. He said "I have nothing against you guys. I wasn't neglected or anything, but, let's be honest I was just a temporary member of the household. You guys are were too wrapped up in each other. Despite being remarried and having another child, that man who I call dad still made sure I was a priority in life. When my half sister was old enough to manage, he would occasionally take weekend getaways with just me. I didn't even have to ask. He should me in multiple ways that I was an individual who he wanted a life long relationship with. With mom on the other hand I actually had to put in more work despite her being the parent."
My wife burst into tear and begging for forgiveness. That's when he said he had to leave and apologized for causing any pain.