My bf mentions a side piece?

My bf asked for nudes and I denied him bc he's gotten them for like two weeks straight expect two days and he tells me he's gonna ask his side and claimed he was "kidding" after he saw I got upset and mad. 🤷‍♀️🤷‍♀️ I believe him. But why do guys "joke" like this on a girl who obvs loves him. And should I add it's been 10 minutes since his "joke" and a I love you and he hasn't texted back lmao