Wife is having an emotional affair

[Alan A.]

W came home around lunchtime today. I was working on some homework. She asked if I wanted to go get something to eat. I was pretty hungry so I agreed. She was texting the entire time. After we were done she asked if I could get her an early birthday present(it's in a month). I wasn't sure I even wanted to get her anything for her birthday. I just told her that she would have to wait until her birthday before I got her anything. Then we came home and she had to leave for her next class. She used to come home right after class but today she never showed up. We had talked about going grocery shopping this evening but it looks like I'm gonna have to go alone. What's your take on the birthday present? I don't really want to get her anything but would that make the situation worse? I know what she wants and it's about $40.