That step #1 is a huge one. Just accepting the loss and calling it what it is. People get hung up going over what could have been or reliving the bet/game etc. Once its passed let it go and move forward. Assess what you need to do to get by it which the op mentions a few. After a huge loss a cooling down period is probably the best thing. Walk away for a bit.
This should certainly be the case in gambling, because one should only participate in gambling if one has the patience and self-control to afford the amount of loss one can afford. There will be losses/gains in gambling and you have to accept it. Of course, if it causes temporary stress, it would not be bad to share it with close friends. By doing these two things - accepting losses and sharing them with close friends - a gambler will not break down mentally because close friends or relatives will be able to comfort him in those bad moments.
Hmm maybe it can be said that one of the requirements that is recommended for someone to have before becoming a gambler is to have patience and self-control, yes that's right I agree with that opinion and maybe I will add another thing which is a gambler must also have a good and responsible mentality and of the three things in my opinion the most important is responsibility because only with that will a gambler be able to avoid emotions when they experience defeat.
Regarding your idea of sharing the bitter experience of defeat to one of your friends, yes that is also a pretty good idea, because at least there is a possibility for your friend to try to save you from emotional disturbances that try to lead you to various aggressive actions, so the most important thing in my opinion is to have good responsibility which responsibility you will only have when you understand all about gambling.