You don't know that. You are dealing with another person who DID betray you and use you! Whether she cheats or not is wholly her decision and life.

No, you can't "get over" her betrayal and make it like it never happened. You can only work with yourself and your thoughts, feelings, attitude, toward yourself and these two others so you are less focused on them (she cheated) and work with her to see if she is working to rebuild your trust (or just acting like the problem is "over" and there's nothing she needs/wants to do to change herself and how she relates to you so you view her as a trustworthy person again) or, you have to decide whether the work with her is too great and you'd rather move on to loving someone else who more willing to do the hard work of becoming/acting like a trustworthy person.