Julia, there is nothing weird about it. Tyler is used to you always being there for him. I have a similar situation here. Before Phillip came along, I was always there for my mother. A lot of the time, she thinks I am being antisocial just because I spend time with my husband. The whole thing is that some times, we cannot give as much love to someone that expects it, when a new love comes along.
You and Tyler are both adults. Perhaps Tyler needs to find someone and learn that lesson. Then, he won't be looking after your needs, or expecting you to take care of his needs as much as he got adapted to.