I've been worrying about something for six months.
Why have you been worrying for so long?
Because I don't want to make the biggest mistake of my life.
There's nothing wrong with worrying about something, but to do it for six months is not healthy, you should talk to someone. They can help to ease your stress.
I've tried to talk to my friends but they aren't very helpful. They just keep saying 'its just a mistake' or 'don't worry it's going to be fine'.
When something worries you for such an extended time, it's important to take a closer look at it to understand why. What is it about this concern that keeps you stuck on it. By examining the problem closer, you will be able to release the worry that it causes.