When my stepson comes home from COLLEGE, why does my wife put our relationship on hold?

She needs to "spend as much time" with him as possible. My concern is that we never spend time together as a family. I am often excluded and end up doing many, many things on my own. Not only am I not involved, its considered insensitive on my part if I am not understanding. Granted, our relationship (the son and I) has never been good, but at least I got them both to understand that there will be no disrespect towards anyone (the type that you generally see with "step" relationships). I knew being a stepparent would be challenging, but this has gotten out of hand. Of note, we've been married 4 years and have no children together. He is her only child. Why is this and how do I handle this?