Heart Attack, Online Affair, Midlife Crisis...

I need advice, I have been married for 20 years, we have a teenager and I thought we were great..15 months ago In May 08 he said "I love you, but I am not In Love with You" ( how tacky) and he wants to find his happiness elswere, but will stay until our child graduates in 2010. I was determined to do whatever it took to make this turn around, in the meantime from then until now, I have ( in order )discovered viagra he ordered online, painkillers as well, Dec of 08 he has a massive heart attack ( he's 42 ) and has surgery, the day I was suppose to leave town for a week, that night I recieved a call from a girl looking for him who thought I was out of town, I did not say anything due to his recovery, I keep that in for the next 9 months only to discover online postings from dating networks he had joined because as he puts it "lost lust and passion" is "married and bored" but yet is treating me really good, I thought all was well and the last thing was a response to an ad in craigslist...I confronted him with all of this and I told him that it is either counseling or divorse, he said he will not go to counseling but cannot leave due to income, that it was all inocent, no work, he was bored and wanted to see naked pictures.. Our child does not know, we are still sleeping in the same bed for this reason, I do not want my child to know until we are certain, I told him he can stay until he gets on his feet...deep down, i want this to work, I have half my life invested with this person...I do not want to start over, but cannot live this way anymore, did I meantion he is on zoloft for depression also...any advice would be great