Feeling down when something horrible happens to you is OK. It's a natural reaction to stress grief and loss. It can be interesting to just sit 'in' that emotion sometimes, let it wash over you rather than being disappointed because you think you should be 'coping' better.
You are only human and humans get sad.
Talking through your feelings with an independent person can be helpful. Many of us have employed counsellors, of one description or another, to get through particularly rough spots.
Personally, I have found great benefit from doing an emotional download on someone who I then pay to keep their mouth shut. Finding that right person can be a bit of a lottery--some of the practitioners I've come across were complete flakes. Which, oddly, made me feel better in itself.
Hang in there, be kind to yourself and get some professional advice if you feel you are in a rut that you can't get out of. Mxx