Jason,
Those of us who have never had to take a life can never fully comprehend your feelings on the value of life. When the Lord is ready even doctors can't change his mind. I really hope you can lighten up on yourself for not being able to preserve a life that was so important to you. It is natural, normal and I believe very good for parents to precede their children in passing on from this life. Having lost one daughter already my deepest wish is that I go before my other daughter or any of my grandkids. Live your life and treasure your mother's memory. I assure you the last thing she wants is for you to do is screw up your life or cause her grandchildren misery over the fact that the Good Lord took her first. Enjoy her memory, celebrate her life. Don't mess your life up over her death. Just because the Marines trained you to take a life in situations that require it, they didn't give you the power to control life. I'm sorry your service to our country put you in the situations it did but I for one am eternally grateful you were there when we needed you. I was orphaned at the young age of 47 and I promise you I felt like an orphan. The hole it leaves is real and large but now at 69 I promise you my life is happier than I ever imagined and it has to do with kids and grandkids. And I know my mom and my dad are proud of what a great grandpa I am, despite their not being here to guide me and enjoy it. Best of luck and please make yourself move onward and upward, a downward turn at this point could be tragic for the ones you love and still have.
Nick