I don?t agree that it is a power thing, it sounds to me like it is really a case of being attracted to you and having to say something or to regret it for the rest of his life. As someone above said, unrequited love can be overwhelming (I know from experience) and you either have to do something about it or try to forget about the person.
It could be one of a few reasons that he told you he loved you, maybe he really thought you were attracted to him by something you did or said before you met your husband or the fact that you have had a very easygoing friendship, maybe he was just shy (I know it took my DH 7 years to pluck up the courage to ask me out as we had known each other indirectly for years without getting together).
Friends falling in love is a very common thing And as someone else has said, he is probably mortified now. (As an example 350,000 Google results for ?I?ve fallen in love with my best friend?).
That doesn?t help you I know, but Love or attraction can be an overwhelming thing and can cripple a person if they don?t do something about it. Just read some of these unrequited love poems www.acedate.co.uk/love/poems/25.php it can really eat at a person. But unfortunately if both people really don?t feel the same, it just causes distress.
I don?t think it is a good idea to tell your husband. It will just cause problems to tell him, It is not like you are deliberately withholding information that will damage your marriage, as you haven?t done anything wrong, its just a friend who made a mistake-albeit a big awkward embarrassing one!
You need to think whether you can still be friends with him, and provided that both of you know that there is no chance ever, then can you go on being friends as you were?