I think it takes a lot of practice to figure out when someone is a good friend.

I would start trying to keep an eye out for balance. If you are the one who is always calling the other person first, always agreeing to do what they suggest while they never agree to do what you want, always helping them with their projects while they don't seem to help with yours --- those are warning signs. Since you have a tendency (as do I) to form friendships with manipulative people, you need to be especially aware of these things.

As far as getting over your friend, I think it just takes time.