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It's for emotional pain, I'm having trouble letting go of a relationship that ended a good while ago. I'm being 'tested' at the moment because he has kind of come back in to my life and I'm worried that I'm going to give in to him and I need to be strong!!!

Why do some people act like YoYo's in your life? It's soo annoying! Just when you are back on your feet and looking forwards, there they are again!
I've been through similar myself, had my heart broken 3 times by the same guy cos I kept weakening and taking him back! But the last time I took him back I was a lot stronger and the first sign of the old "I'm fed up with you" routine and I was off!

I'd done it! I'd "got even" if you like and it felt great!

Never looked back since that day!
Anyway, it sounds like the crystal you have been given is a Serpentine. This is a healing stone and encourages calm and a sense of inner peace. Just the thing for emotional trauma's.
I echo all the advice for cleansing and charging so nothing to add there except you have to believe the crystal will work for you. Put a little faith in it and this will encourage it to help you even more.
Stay strong girlie! You can do it!
Love & Light
Lioness