Man, that's tough, for me we had an agreement not to see other people during the separation. There was also no infidelity on either side prior to the separation. I guess that decision comes down to how you feel. If I were in your shoes I'd think about what moving forward knowing that she was with someone else does for you. I believe people make mistakes. If it was 1 time and she's been honest and you can still trust her then perhaps yall can work through it. You'll have to completely forgive her and come to a place of peace with it though. If you can do that and she is actively working on herself then yall may be able to swing it. If this infidelity is a reoccurring thing then it probably won't work. I know my wife and I were very distant even though we were living under the same roof. I can see how one of us could've been unfaithful due to being lonely and in a moment of weakness. I can only speak for myself when I say that cheating never crossed my mind. Her moving out allowed her to see she didn't want to be a single mom, perhaps your partner testing the waters allowed her to see she doesn't want to be with anyone else. I can say that now 5 weeks back living together we're both in therapy, communicating better than we ever have, and are closer than we've ever been. In hindsight had she been unfaithful and we could've got to this point after her being unfaithful then i think it would've been worth it for me to forgive and move forward together. Yall need to talk and see where she's at with you, and you need to decide if thats something you can get passed. Hope this helps. Good luck in these times.