How am i supposed to react?

While my fiance was sleeping i saw his phone light up with a text. It was from a number programmed in his phone as "aunt dana" and it said...sorry i was at work...n i been thinkn bout u..i had never heard him mention his aunt dana except for once when he was telling me he had relatives in NC. So i felt wierd about it...mite be because the area code was ours not NC. So i reverse look up the number and got some mans name...no help. When he wakes up i tell him about the text but i dont let him know im suspicious. He walks outside to smoke and comes back and tells me that he called the number but he must have put the wrong one in his phone because some girl named kristina answered. Ok i forget about it until the next day when i get on the computer. His facebook was still up and there was a notifucation saying kristina had accepted his friend request...dont kno why i thought it mite be the same kristina but i just had a gut feeling...i then remembered that i could log in to my wireless account and view the phone records...after i figured out how to pull up his records i see that there were several calls and texts to and from that number. I go back to his facebook and look at her profile..it only took a second to see her status said she had done community service at the same place and time as my fiance...by now im feeln pretty crazy.. I look at the phone records again and see that the texts/calls started on the community service day and continued sporadically over the next three days and then ended after he called her the night he told me it was a wrong number. I confronted him and he admitted that she had flirted with him and that he was flattered and he began texting back and forth with her. But that he had felt bad and had told her to stop textn him that night. His phone records pretty much backed up his story and i kno that he hasnt been anywhere without me in order to have cheated. But he doesnt understand that trust was broken somewhat when he tried to cover this upHow am i supposed to react?
I would have done the same thing. You weren't in the wrong. Since he's your Fiancee you have the right to check that **** out. Honestly i would have just flipped out on his ***.