Is it normal that i'm experiencing these homicidal thoughts?

My ex girlfriend and I haven't talked for six weeks. We began talking again and she asked me if the offer still stands that I will be there for her if anybody hurts her.
One guy who lives down my street dated her, and he showed her his dick. He then kept asking over and over for her to show him her tits. She gave in. The day after he broke up with her. When she told me I began to cry, I cut my leg with my knife out of anger and I didn't feel a thing.
I know the guy's exact house, and I have a history of being hugely protective of my ex. She isn't the only girl he's done this to.

To my question... Is it normal to experience severe homicidal thoughts in this situation towards the guy? I'm sorry to say that I have really thought about what I would do, and I'm actually afraid one night I'll snap and kill him. It's not that I would regret it, it's that I'm afraid of how much I would actually mutilate him.

The guy has gotten into trouble with law enforcement, but I know he is still at his house, I also know where he hides his key.

Again. Is it normal to experience serious homicidal thoughts in this situation towards the guy?