He's obvioulsy very insecure about your relationship with your husband. He's also young and hasn't dealt with this kind of thing before. It's crucial to get him to talk about his feelings. You've got to make him understand that you don't want to be with your husband and that he's got your heart. But he's also got to know that there will be occasional contact with your husband, because that's how it is. He's got to try to accept that. Don't forget that you're dealing with a young and inexperienced guy, as mature as he may seem to be around you.