How can I cope with my fiance's flirtacious ways with out getting in an arguement??

We have been together for 5 yrs and he has had somewhat of a cyber affair before. Now there is another girl that he works whome he texts on a daily basis about work stuff but with flirty lingo! He also rides the work shuttle with her everyday. I can't stand it but i am sick of confronting him about it cause he has started deleting the text messages from her so I won't see them.