Why is he such a secretive person?

What do I do about my secretive boyfriend’s habits? He always hides his phone from me whenever he gets a text, and says it’s personal, which shouldn’t bother me but does. I have no such secrets from him, and he says that is my prerogative but not his. I understand that personal boundaries are important, but we have been dating for a year-and-a-half so I don’t know why he can’t be as open with me as I am with him. Is this something I should worry about? I don’t want to be the person who wants to know everything about his life, but I find it strange that he can’t let me know who is texting him.
If it bothers you and you find this secrecy troubling, you can insist on an explanation. He is right about boundaries and the need for personal space, but not if his behaviour causes you to doubt him in any way. When that happens, the onus of reassuring you is on him. He doesn’t have to disclose anything he doesn’t want to, but there also has to be a reasonable explanation for why he is doing what he is. Tell him why this is leading to an erosion of trust, and how it will impact your relationship, so he can take it a little more seriously. If nothing changes, you should worry about whether he sees this relationship in the same way you do. At that point, a more serious discussion will have to be called for.

My girlfriend keeps saying she is not happy in this relationship but, when I tell her we should end it, she refuses and says we have to try. I am tired of trying because I don’t know what she wants. What should I do?
You should tell her that you don’t want to try anymore because this can’t work if one of you isn’t committed. Unless one of you identifies the problem, staying in this relationship will only cause you both harm.