Understanding and handling are two different things
No human being is perfect and each friend is different. You may even have a friend who has issues. You try to be understanding but you get upset in the process.
Understanding and handling are two different things. If a friend has a problem understanding something means you will feel bad for that person and know that they are acting that way becausee of their problem.
Handling something is when it effects you. For instance your friend suffers from anxiety and depression and will go into a mode where you do not hear from her. You understand that she has problems but when it happens over and over again, it will start effecting you.
If your friend is older and still has a curfew you could understand but it is also not fair to you. If you are outgoing and like to socialize this friend could stop you. You will soon feel that you are missing out on life because of that friend and you do not deserve it.
Just because something bothers you does not mean you do not understand. You could still be this person's friend but maybe from a distance. Do not put all your energy into a friend who is not stable. Be nice to this friend and when she calls you, you could see her but also look for other friends. Look for friends who are more like you and make you feel that you are living, instead of making you feel that life is passing you by.