what ever you do just avoid being stressed as that is the most thing that can delay your circle and is even wrong for your baby if you are preg
Firstly, I am so very sorry to hear about what happened to your boyfriend, that is absolutely awful, I'm really sorry :(
If you take a test on the day after your period was due, you may not have had enough of the prgnancy hormone in your urine for it to show a positive result. I would take another test in a couple of days.
Stress can certainly play a roll on your menstrual cycle too, so just repeat the test in a couple of days to confirm. If that's still negative, and you don't get your period, I would go and see your Doctor.
Hope that helps. And once again, I am really, really sorry for your loss.