confusion

Writing in journals was once a forte of mine. However, in the past few years I seem to have lost the ability to write down the events of my life and thoughts thereafter. There are times in which I will pick up a pen, open my locked diary, and write down the cascade of events that have befallen me. Usually these events are life-altering to some degree. Lately I find myself writing in my diary often, and almost always find that my entries are about my boyfriend.

Why am I confused?

I received an email on facebook. Prior to receiving this email, my boyfriend had been complaining about one of his ex's that would not leave him alone. He called her psycho, obsessive, etc. The email I received on facebook was from her. It was very detailed and contained valuable information. Basically the bitch stated that she is in a relationship with my boyfriend, they are sleeping together, and when he is not with me he is with her. This confuses me and makes me nervous. My boyfriend has barely any free time, let alone any to drive 20 miles to see her. My boyfriend is also a little cheap so I don't know why he would pay gas money to drive to her. I trust my boyfriend but I am confused and nervous. What if this woman is not lying? What if my boyfriend really is cheating on me? How do I find out the total truth without breaking the trust bond I have with him?