I once had a boyfriend. He once read my journal. He read all about me sleeping with another man. I no longer had a boyfriend.
In the end, it helped our situation. The relationship had been over for a while, for me anyway, and I was too much of a coward to confront it. Walking away would have been much more noble than the cheating, but I was twenty-two and hadn't learned that lesson yet. In my ex-boyfriend's defense, he did what he had to do. He was not an ever-doubtful type of guy. He didn't have my voicemail access code or my e-mail password nor had he ever asked for them. This came about because, to his credit, he knows me very well, and he sensed that something was very wrong. He confronted me twice. The first time he asked me what was was up. I answered, "Nothing." The second time he asked me if there was someone else. I said no. He knew better and rightfully sought evidence to support his unwelcome theory.
Someone potentially reading a journal is one of the reasons many people don't keep them, and it is certainly a dangerous aspect of the craft. It is not, however, the most dangerous aspect. The most dangerous aspect is telling yourself something you didn't want to know. We, as human beings, lie to ourselves all the time. It's very strange and counter productive. We'll tell ourselves we like job when we don't. We'll tell ourselves we're in love with someone when we're not. We'll tell ourselves we aren't attracted to a person when we are. So to me a journal is that place to be unabashedly honest with yourself, and it's dangerous because you won't always like what you see. You'll look at your thoughts and say, "I don't actually think that do I?" You do and it's fine. Admittance is the first step in anything. You have to admit to yourself you have a dream before you can pursue it. You have to admit you have a problem before you can solve it. So I say write openly and honestly. Burn the pages if you must, but first confront all that is going on in your mind.
If you're not sure where to being with writing a journal OR you simply enjoy reading other people's journals, check out my book Note To Self. Here's the trailer (ex-boyfriend and all):