The best advice is - if you are not absolutely certain that what you are saying is going to be really helpful, then say nothing at all.
The best support is listening - being a sounding board while your friend puts complex emotional thought processes into words, and in doing so, starts to formulate solutions and plans moving forward.
You are not responsible for sorting this out - being a friend is about support, which is not the same as answers.
Be available to listen, be honest if asked, and only if asked, and otherwise, don't let it take over your life, which helps no-one.