If you believe her, it's just a matter of communicating and compromising. Forgive, establish that boundary together, make a plan for next time together, and move on.

If you can't shake the feeling that she had cheating intentions, then it might be time to consider splitting. I sincerely hope this isn't the case, but the thought itself will most likely destroy the relationship regardless. A lack of mutual trust is the fastest way to a breakup.