In order to overcome a big loss from gambling you need to do 2 things:

1) Take break and try to understand what went wrong. In this stage you will cry like a baby, tell yourself that you a piece of shit and all these self-destructive activities.

2) Understand that shits happen to everyone and it is a very natural think. Truly understand that you are fully responsible for your loss and no one else. Take you loss and deal with it. It has happened you cannot undone it,no one can.

3) Correct the mistakes that you have done and try again. This time you need to put processes which will stop you from doing the same mistake again.

Good luck. Life is unpredictable, shits happen to everyone, learn from them and become stronger. With time you will build confidence because of the shits that you have overcome and you are still here and fighting.