Well me and my fiancé had a break a few months ago and she started to fall for this guy who happened to be both of our friend: and he just told her that he loves her and she told him that she loves him too and right after we got back together she was visiting him and she cheated on me. Now I don't know what to do I'm so confused and I want to look at her phone to see the texts that he is sending her but she gets all defensive about it and I'm not going to lie I'm scared and threatened because I'm going to be enlisting in the army here in a few months and I just don't want anything to happen between me and her.

If you don't trust her brake it off otherwise it will only cause you future problems if you don't. You may never fully trust her again and I'm not surprised but she seems to be confused as well but that's what I would do. You can't spend your life worrying and getting all paranoid, its not healthy I say she's cheated, move on, she ins't worth your time

Something has already happened between you, she cheated, and you lost trust in her, and you think they are still in contact, and you have to leave. Do I have it right so far?

Explain to me what your point of continuing with someone who cheated while you are still there. What makes you think she will be faithful while you are gone? When you leave for the Army, leave her too. Better yet, leave her now and be really ready to leave for the Army.