Honestly, I would give notice. He's not learning and this one little child is getting hurt. I would assume that childs mom is upset and may leave if this continues. Who would you rather keep? the biter or the bitten? It's not fair to the other families. You have to look out for the good of the group.

I've had to term a 3.5 year old due to bullying. it was hard because I loved this child and the family, but my setting wasn't working for she anymore and the other kids were paying for it.

It was messy to term them but in the end my group became much happier, and the parents really appreciated that I took noice and then took charge when things didn't change