Op, I have been watching this thread all night 
and re-living my own experience.
I just want to warn you: no matter what you are told, or what you accept or what you choose to believe, nothing will be the same. Ever.
You deserve and need all the time and space to quiz your H, interrogate the timeline, consider your choices, but please be prepared for your life to be turned upside down. I wish you every courage, strength, resolve and resilience, because you will need them. And if you - like me once upon a time - accept an offer to try again and rebuild your relationship, please know that doubt and betrayal are so corrosive that the person you were yesterday will be a distant memory. Regardless of what your H says, be mindful that your personal clock has got re-set from today, and your future wellbeing depends on how you act.
Although it may not seem this way, in the blur and the upset, your future life depends on your response. Please consider what advice you would give to a sister, friend, niece, daughter in your shoes, and apply it to yourself. Do not prolong the pain: the hurt you felt when uncovering the message is palpable. I am not saying LTB in a reactionary sense, but do please save yourself further heartache if you know in your soul that this is too much to bear