I have to disagree with you that 'a reckless act is a reckless act'. In the case of reckless driving, in the majority of cases it does not end in the death of their partner .. it might do in some instances, but 9 out of 10 times it won't end in anyone's death and that's generally why they do it is because they know it probably won't (not that I am in any way supporting the kind of stupidness that can end up with someone being killed as a result).
In the case of OP, he went into that bathroom, armed with a gun which he knew was loaded with bullets designed to cause maximum possible injury and which would result in killing whoever they hit, and he shot blindly through a toilet door without having first checked to make 100% sure that it was not his girlfriend who was in there (if you believe the 'Oscar's Fairytale' version). So, in this kind of 'reckless act' which will 100% always end in the death of a person, you make damned sure it's not your girlfriend you are going to end up shooting.