@deatask,
Get your husband into counseling. He needs treatment because his (likely) depression is going to pull everyone else down with it. You say he engaged in questionable business dealings. You need not answer this next question but consider the answer in your head - does he manage your finances (e. g. balance your checkbook)?
I think the feeling of attraction is kind of normal. You had positive attention paid to you, and it was for something in your life that brings you joy. Big contrast, too, to your husband who seems to only be able to handle happy talk. Well, life is not like that. Like you said, your daughter has needs (as do your other children, as do you). Ignoring these problems is not making them go away.
If your husband will not go to counseling, then go alone. Spend the time getting tools to cope with someone in his condition, and to figure out what you want to do. I doubt that your future is with this guy at the conference, but you may find that your future is without your husband.