Gms, no one is responsible for a person choosing to commit suicide, no one can make other peoples choices for them, whatever they are, however bad you think those choices are and however painful. I'm sure as you have suffered so much after your step fathers death, you wouldn't want to put your loved one's through what you have been through?
You sound like you are a very compassionate person, I'm sorry you are in so much pain at the moment. I hope you can find some peace in yourself soon