I do not know about reasonable - feelings have precious little to do with reason! I think the point here is that though you might feel possesssive about someone, you are not entitled to kill them.
Having said that, I wold like to speak of a situation of my own many years ago. My then husband found another woman, did not tell me about it, lied for two years, took her into our home for Godssake, in our own bed..It was never a home to me after that.
I had all the emotions people have in these situations - I could not take it in, had no idea, could not - would never ever in a million years have thought that he would lie to me, felt invaded, confused - the pain was killing me. I also felt angry. In fact, a white hot rage. I had fantasies - many fantasies - about getting a gun and shooting him right between the eyes..I had it many times, and it helped me.
It is hard to get a gun in Denmark, but I might have if I tried real hard. That would have made it premeditated. What would have happened if I had actually done it?
Let's see, I would have killed a man I actually still loved. I would have caused his parents and 4 sisters unspeakable pain, people who were completely innocent. I would have caused my own family pain. I would have spent the next 4-16 years in jail. I would not later have met my two other husbands, who I love more than anything in the world, and would not loose for worlds. And I would not have had my stepson.
I guess thats my point. You have a right to the feelings - to any feelings. But not the right to kill.