How do you handle ups and downs, she changes a lot.

So I have been semi serious with this chick for 3 months now and she always cycles her behavior. She knows she is like that also.

Example: If she is busy and not answering me, she can apologize and say she is busy and will write me later with some nice remark. A week later with the exact same situation she just won’t answer until the night and when she does she ll say nothing about it.

How do you handle this, am I supposed to just not give a fuck? How can you build a relationship like this though - can you?