Ironically enough, you might find the trust has been damaged far more by his lack of honesty last night, than the original incident. Pragmatically, I'd advise you to be very vigilant because there is a reason he doesn't want you to know the truth.
Charbon, I think this is right. Even now, after everything is out in the open and apologies all round, I still marvel and feel horrible that my h was able to lie to me so frankly, and for so long. Just remembering his face, particularly in the last few weeks, swearing to me that if he could possibly put me out of my misery by telling, he would. Even at Relate, for nearly a month.
They then manage to tell themselves that it would be unfair to tell, it would hurt you too much. My h finally confessed after two incomplete half goes (eg I did receive photos, but men sent them of their gfs). I had passed him a note after an 8 hour conversation saying, one the first side of the page, 'you are not lying to me because you think the truth would be too hard for me to hear', and one the other side of the page 'it is because you cant bear for yourself to tell it'. I walked outside and left him to think about it. Then he told all.
For me, in the end, it came to a point where I was willing to ditch my 20 year marriage in order to hear a story which felt like the truth to me; I had drawn a line. That was scary, in a way, and a small voice was still asking if it was too selfish to others, eg kids, over something quite small ie he wasnt having an affair, as far as I knew. BUT at the end of the day, a lying husband is a lying husband- we all deserve more respect. And anyway, the man loses out for himself without trust- because lack of trust makes us all hold back something to protect ourselves, even subconsciously, and so everyone loses.