Long story...proceed with caution..but really need advice?

There is much more going on than he's telling you, and it's not just hiding a number - and he very successfully diverted your attention from that - but the words he used in his email "I will live. Don't e-mail back please... you know y". Is this something you would email to a coworker or casual friend? Think about it again. He's cheating, I bet you $100 on that, the very least its an emotional affair.