It sounds like you know what you need to do -- it's all a matter of doing it.
My H had several affairs over the course of our R (before marriage and once during). Each time, it broke my heart into pieces...and all it took was the smallest hint of an affair and I would lose my cool. What I needed the most during those times was complete and utter honesty, open communication (willingness to let me talk it out, ask questions), and compassion for the fact that I felt betrayed (even if I wasn't). Unfortunately, my H was never very good at any of those things and would just get angry when I accused him of something he didn't do. Sure, I can see how messed up it is to be blamed for something you didn't actually do, but the flip side is that there's a reason I didn't trust him -- and it didn't help that he would sometimes lie to cover up the stupidest of things (much like you did), which only made things worse! ARGH!
Sorry, just a little vent there. I hope you guys iron things out. I hate to see this happening to you; you're such an inspiration!
