What Causes Vaginal Bleeding After Having Non Penetrative Sex?

Hai my boy friend fingerd my vagina today and he made me cum and when he removed his finger we found blood on this finger. Later I reached home I went pee and again saw blood coming. I'm really scared when I spoke to him about this he told me due to some scratch by nail,even though I'm scared.I'm 26yrs old
Plz reply to me at the earliest.
Thank you