Not being there will also be a weight on them. Being there is the better choice.
Explain, if they're old enough. Find help (online or offline) in finding out at what you can explain to them. Find help to get rid of your stories without having to tell them to your kids if you don't need that.
Being afraid comes with the territory I guess. Acknowledge that. Accept it. Explain it. Explain that you cannot always acknowledge or accept it. Accept that you cannot always explain it.
Do your best, how messy it is.
And maybe you know all this, maybe you do all this. I don't know you, don't know your story. But it is as it is. You cannot give them another father. You probably cannot change how you feel. So they have to live with it, as you, and find a way.