This sickness you feel is due to the thoughts you have running inside you. What may help is learning that how you feel is based on the thoughts you have; start to think of other thoughts; in time, if the new thoughts are positive; you begin to realize you feel better; it is a process that takes time.
For me, when I learned that the woman I loved took her own life, it hit me hard. I loved her; I knew she was not dealing with life well. She kept telling me, when I was with her, she felt calm. She had pushed me away. I had been urging her to see a counselor for her depression; she kept pushing that idea off. So, for me, the self-questioning of "what could I have done to stop her?" It runs through my mind. It causes me distress.
I have learned some things. One thing I accept is that I have no control over a person who is suicidal. I may have been influential, but I can not stop someone intent on ending the pain they feel with the final solution. Because I know this, I say to myself, she is gone forever, questions are moot. When I think of her, I repeat my mantra to myself.
In time, and using such mantra repetition, I begin my healing process. I was, like you, in the first stage, feeling sick, because I felt I did not do enough, or did not do the right thing, or did the wrong thing, or, or or, whatever it may be. These are insane thoughts, based on the belief that I could have influenced the outcome. It is arrogance on my part to believe I had any power to change what she chose to do.
May time begin to heal you. I hope you could talk with people enough, to learn that you are not at fault. This you must understand and convince yourself of such. May you feel peace once again.
Good luck to you on your life journey. I think of this in analogy terms. This experience is a chapter in my life-book. A new chapter is started. The page is turned.