@Juliet1987,
I have no idea what to tell you. You have already made up your mind that he is cheating, and you already don't trust him. Your marriage is over.
So why not save some money and fire the private investigator? You already have lost the trust you had for your husband, so even if he's utterly innocent, it's all over but the shouting anyway.
As for the "he have [sic] my heart in control" bit - you're a grown woman. Unless you're being abused, you have control of your own heart (and if you're being abused, you often have control as well). You are 30 years old. Take back control.