Why is my wife so upset over my son?

Married my wife 3 yrs ago. Was divorced from my ex for close to 9 yrs. I have 3 kids, two are doing their own things. My youngest is 16 and I still get him every weekend from Friday-S unday. I pay child support every month. The problem my wife is upset because every weekend I make plans for him and I to do things like fishing, hunting, shooting birds, basketball, darts etc. HIm and I will watch tv together and just hang out. My wife says she feels like I spend no time with her, she can join us whenever she wants. But my son hates her and I can tell she is jealous of him. During the week we dont have time to do anything because we both work and usually spend 1-2 hrs together watching tv. She complains constantly because I buy him whatever he wants and yet continue to pay my court ordered child support. She said within 5 months I spent over $500 on him on top of the child support. When she says something to me I get upset which makes her even madder she says now I am ignoring her when I get mad at her but only when my son is here. She has been very respectful to my kids, went out of her way for them and never disclipined them or corrected them, she only tried to be their friend. But they hate her because of my ex. I cant understand why she cant see that "kids come first". Am I wrong? She said kids come first for food, shelter and proctection not spoiling them.