Troubles from the past!

Sooo to build background I have been cheated on several times in past relationships... whether it’s my boyfriend flirting with a random girl behind my back or with my best friend or both of those at the same time.... Well, I really don’t know how to get rid of the fear that it’ll happen again. I tend to ask my current boyfriend a lot of questions and I’ve set some pretty strict rules, but I hate being so bitchy about it so I tend to act like nothing bothers me and let him do his thing. I don’t like to be known as the controlling girlfriend and also I want him to have his freedoms plus I do trust him! He has yet to lie to me about anything that would really upset me... so I trust him but there is a fear... how do I help myself get over such a fear?