I'm sorry you're going thru this. My wife had an affair last summer, so I know what you're going thru.
I see where this has been going on for awhile now. Tell me, what were the consequences to your husband for having an affair? Have there been any? What do you plan on doing if he goes away for this weekend?
I'm not the typical DB'er, but to me, just based on the limited things you have posted, I think you may be giving him tacit approval for what he's doing. No, you can't STOP him, if he's hell-bent on having an affair, but there are certainly things you can do to make it a HELLUVA lot more difficult.