Why does your anal hole get wider sometimes after having vaginal sex?

Sally • I'm on here for calculating my period. I'm 25, love dancing, music, and food. I work as a chef🔪🍋 Robby holds my heart❤️🌹2020🌹
So I recently found that sometimes my anal hole is more loose than other times. Yet it is normally very tight. Can someone explain to me why sometimes it loosens up with out my noticing? And how does that happen? Cause it seems like it's after I dildo hard vaginally. But I'm not sure that that's the cause.