Condom trouble

Brooke
Okay so, I was having sex with my boyfriend and I was on my period. We were using a condom and after he came, he looks down and goes "where is the condom?!!" Ugh you guessed it. It came off. Inside. Me. Embaressed and freaked I hobbled off to the bathroom to retrieve it. Has this ever happened to anybody else? Why and how can I stop it?