That won’t last long and soon everyone will know
You had bought the lingerie for your wife as a birthday present, and although it had been a long time since the last time she'd permitted you to have sex with her, and although she had been cuckolding you for even longer than that, you still hoped that *maybe* -- when you saw her putting on the lingerie -- tonight might be the night when YOU finally got lucky with her again. You were wrong.
The first thing your wife did when agreeing to cuckold you was to cage you. And she did it smirking. Now weeks after she's hooked up with two men for sex and is embracing your cuckold status. Now seeing her around the house you grow frustrated being locked up. She's teasing you and making you hard displaying her body making you crave her so much more at a time when she's enjoying other men. Cuckoldry is cruel but you're not complaining.
The fact that you are helping her buy clothes so that she will look pretty and sexy for her boyfriend is humiliating for you, but at the same time, at least you get to see her in the clothes when she first tries them on before you pay for them.
Of course, you know that you don't REALLY have a choice, because you know that this is what your wife wants, and when she wants something, she always gets it. And right now, what she wants is to make you her cuckold.