Hi, LaraKeziah! I'm hesitant to post because you've already received good advice. I'll try to be concise.
You can help out your counsellor by making a few notes beforehand; I suspect they'll want to know about times, contexts, contents, durations, etc. BUT...ultimately it is the counsellor's responsibility (not yours) for getting to the bottom of things.
Wait. Let things clear and take better shape. Then, when you feel comfortable with the information and yourself and your friend, you can reveal as much or as little as you want, and do so all at once or little-by-little over time. You're in charge.