That is a tragedy indeed, not a situation or event, beyond that. I really feel for you, which I admit I can be incapable of doing sometimes, to be honest.
I'll be blunt and not pretend there can solely be positive things you can do without ignoring the inevitable negatives that comes with such a tragedy. But there are things to help, of course, but I feel it's also best to be knowledgeable (let it be obvious or not, I just want to make sure by informing you what I know of such) about what cannot be prevented.
Grief and mourning is obviously going to be inevitable (duh, it's already happening). It is honestly not something you will truly get over, but time will help at least forget the frequency of the memory. It can also dull the extent of the pain but not enough as to view it purely objectively. It will stay with you forever, but I find with a likely long-ass period of time, the pain is quite faded away to the point where it appears not to be a difficult subject to talk about unless you are traumatized, as unintentionally callous as that sounds. The overt, acute pain (upon reflection) will still probably be with you for longer (how long cannot really be answered) than most typical loved-one deaths given the very unfortunate situations behind this. That's a component of death, to guarantee the necessary pain in life. And by necessary, you can view it as life-destroying by how you react or you can view it as a way of making the happy moments even more profound due to the increased contrast. Even if you have an inclination toward the former, please do everything in your power to habituate yourself to the latter way of thinking.
Obviously time is the greatest healer. But not quite entirely heal in the traditional sense as there will still be scar tissue (which fade away as well but stay with you regardless). There is not much to do but to simply wait out the ride. If done right (which I will address as best as I can in the following sentence(s), it can be quite a healthy and life-changing experience. I'm sure you already know the basics of that, such as therapy being helpful, talking to other family members, etc. What I can say for sure though, is what NOT to do.
-Do NOT self-medicate under any circumstance, this will interfere with the grieving process and guarantee you a ticket for an even worse ride by having long-term negative interference. And of course, the tendency to reinforce the possibility of addiction.
-Do NOT avoid the subject completely (sometimes is fine, if it gets extremely overpowering). It is okay to think about this. Don't deny or ignore it entirely as tempting as it may. I have done this and it hurts me a lot more long-term compared to the situations where I did stare the pain in the face without fear. I personally don't think avoidance is necessarily a good thing. Recognizing your pain, the source of your pain, and reacting to it how your body/mind wants to (which is variable in certain individuals and circumstances) is catharsis. Catharsis is absolute key. Not repression.
By the way, plenty of philosophy will most likely come to you, the type of philosophy that can be conflicted and contradictory but worth taking into consideration the most out of others' (not that they aren't extremely helpful and to be ignored) as it is applicable to you in and of itself. I think the philosophical justification tend to go away once grief has dissipated though, as the subject is infamous for being amongst the most complicated and irresolvable to the point of not even bothering anymore. This isn't a guarantee, most of what I'm saying are just possibilities; it surely true that you do get a deeper insight to life based on the fact this is such a unique experience amongst others, and it is easily a situation in a life to learn from this and better yourself in many ways (dealing with stress, having deeper insight as to the possibilities of life, having a more intimate encounter with death as to make you fear it at least a little less, etc).
Look to the future.
I hope I helped, if I didn't, I apologize and tried my best to do such, don't take it personally.
My condolences.
![:\](https://bluelight.org/xf/BL_Images/Orig_Emoji/wrygrin.gif "wry grin :\")
