I heard a poll once that asked what people were more comfortable with: a person in an open relationship or someone having an affair. More people said that they liked the person having the affair. I think the basic idea was that the affair person was trying to be faithful while the person in the open relationship was not.
I think it is just cultural. Hopefully this guy you like is just thinking things through. It is hard for someone to accept a new viewpoint, even when it is purely logical. If he has problems, I think you should present what you told us to him. If he can't accept it, then you may have avoided a lot tougher issues in the future with him.
I think it is a good idea to try to get him to be open with his wife. It may cause some short term pain, but it will probably be better than if she found out some other way.
I hope it works out for you.