I'm sorry to hear that, just remember that your are not the first and won't be the last person to whom that happens. As long you don't hurt anyone, including yourself, it is ok to express how you feel. Let yourself a mourning period.
Telling to the people you can trust like your family is good, they can listen to your grief, cheer you up and advice you in case you want it.
About that girl, she can go to hell, basing in your text, I suppose that she was the one who began the cheating, and your friend fell for that.
About your friend, if you can't forgive him in this moment, it is valid and also it is valid that you cut temporary contact with him until you feel you can talk to him again. Meanwhile, ask yourself if your friendship is worthy. Once you feel you can talk to him, you can talk to him again.
How long have you been friends?