This relationship isn’t working out and doesn’t seem to have a future because of the problems you’re having. Specifically, that you fight half the time you’re together, after a year and a half relationship, and she is so distrustful of you even though you haven’t given her any reason to not trust you. The mistrust she brings to the relationship is based on her past, and her insecurity at being 11 years older than you, which doesn’t help her fear of your leaving her or cheating on her with another woman.
No matter how much you love her, if she isn’t able to be peaceful with you and because of her history of being cheated on, which she hasn’t resolved, you two fight over half the time you’re together, you have to accept that this relationship will never be a good one for you. And to make it worse, to avoid the fighting, you’ve started withholding information from her that is innocent — but that you feel will start her jealousy and anger up. If you can’t be honest with her, you’ll never have real intimacy, and ironically, you’ll look for other people to talk to about your deepest feelings because you won’t be able to talk to her. And that [i]will[/i] be cheating.
So, accept what you have for something that was great while it lasted, but isn’t going anywhere positive, and move on. I’m sorry because I know this will be difficult for you, but it’s for the best.