What your going through must be tuff. I hope your talking to your friends and family about your less fortunate mistake. Talking it out helps relief some pressure from yourself. Another way of thinking is that, this mistake happened in order to have avoided a bigger mistake. Changing your perspective will help and I know you can do it.
If you mean wrong decisions, if you talk about mistakes, then it is very simple. Find out why you decided the way you did. If it was a lack of knowledge or wisdom, then you know it now and will not make this mistake again. If you have made the wrong decision because you are you, then learn to accept that it will happen again.