Periods and sexual acts

A couple of weeks back i had my period it was like day 3 of my period, my boyfriend and i act sexual but we never do anything like sex. 
​Anyways, on this day he was doing what we usually do, like the rubbing and stuff like that but too me it felt so wrong and quite disgusting, he could see i was uneasy about this and he said "i know you find this disgusting but whats so bad about a little blood?" 
​Quite honestly i dont know what to do, he is the perfect guy and is so understanding.   When ever i tell him to stop he will but i couldnt bring myself to do it this time ... Help?