If you are intent on killing someone, you going to try to do it no matter what your status is.
But, I would say that if you into taking your relationship seriously and want to start a family and get married, you are much less likely to kill your family members. My bet would be that statistics would bear this out.
Unfortunately, some people don't realize the commitment of marriage that they are entering into and resort to some absolutely damaging behavior without the other party involved knowing it.
Scott Peterson!