60s/70s biker rape revenge movie

Hi all, this is a movie I caught on TV years ago and I remember quite liking it.

A young (hetero) couple are attacked (I think in a graveyard?) by a biker gang. The man is knocked out and when he comes to, his girlfriend confides she was raped. Most of the movie is about the shame and recrimination each partner has about this. The movie ends with the biker gang returning and the biker gang leader and the boyfriend stab each other simultaneously.

I wonder if anyone knows this one? Thanks very much.