One thing to consider is that you have known this friend as a friend. That means that you have probably seen him when you were doing fun things together. Its easy for someone to seem more interesting, more fun when you aren't seeing them every day, when you aren't doing chores, being sick, etc. You really don't know what it would be like to live with him.
I have a female friend (I'm male) who seems fun, interesting, exciting. I'm attracted to her, and some part of me thinks that I have deep feelings for her. When I think about it though, I realise that while I really like her as a friend and enjoy her company, there isn't really a deep attraction, just a bit of infatuation.
So - first I think you really need to examine you own feelings. Do you really think you love him - or is he just a really good friend who you happen to be attracted to? Love and lust often go disguised as each other, but they aren't the same.
If you really decide that you love this man - then the kindest thing you could do would be to leave your husband so he can find someone who loves him. More likely though, you will realize that much as you like this other man, you don't really want to spend your life with him. In that case, stay friends, and avoid situations where either of you might do something you regret: don't be be alone and drinking with him for example.
This sort of situation is really difficult - can be a tremendous strain. Just remember that as someone on this board said "the grass is greener on the other side of the fence, but the cows poop there too".