period blood or hymen broke?

My boyfriend was fingering me in his car, nothing unusual we do it a lot; im still a virgin though. And I never bleed.
He ate me out and fingered me, it was dark so we couldn't really see what we were doing and when i got back home i found out im bleeding
I was already 3 days late to my period andy period is pretty regular so I expected it at any minute. When he got home as well he found out that his hands are bloody as well.
I'm not worried that it's my hymen I just need to know what it is. Please no negative/hate comments.