How do I know that I should give up on her?
You should give up on her when she shows interest in another guy. In addition, you should pursue her within reasonable time, after which it means that she is not interested in a relationship.
When she acts like she doesn't care anymore. And if you can tell that she doesn't really care about you.
Sometimes a girl can act like she doesn't care when she really does! Give it some time then if shes really not showing interest she keeps ignoring you, then its time to move on!
When you are the only one putting effort into staying together and making things work.
It's hard to say. Do you mean she wants out of the relationship? If she does, you have to let her go.
When you know it's completely hopeless
i need a little more explanation here bud
You should give up on her when you find yourself asking the internet when you should give up on her. *hint hint*
You need to talk with her. It's easy to give up and harder to talk. Either way you don't want to be left with regrets. My opinion.