Meth is a powerful drug. So is crack or any other form of cocaine. Heroin is a particular sort of hell.
An active addict will do whatever it takes to maintain the addiction--regardless of who they hurt. Spouses, children, friends, parents, co-workers, bosses, it matters not to them. Anyone who gets in the way of the addiction is the enemy--anyone.
I'm sorry you were hurt by your friend, but I'm afraid I'm not surprised by this behavior.
Please take good care of you!