I know what you mean by being frightened about what your spouse is doing, if indeed the MLC thing fits.
My wife was acting strangely, just like your husband is: a weird kind of affection, coupled with some sort of blind insistance that you should be OK with their "friendship," added to all sorts of behavior of wanting their cake and eating it too.
I would dig in your heels for a hard ride. I don't think ultimatums will help, although setting certain limits might.
A page from my book - my wife has 'realized' more than once that her "friend" is a ambulatory disaster. But she has gone back to him almost as many times.
She's recently told me that she's felt like she was "in a fog" with her relationship with him, almost as if she were drugged.
(And keep in mind that I've never mentioned any of the popular literature comparing adultery to addiction.)
When she has some clarity, she sees a value in working on our relationship. But in that "fog," she might just as well be in a netherworld.
I don't think the affair is the whole picture - our problems and her problems contribute to the general malaise - but there's nothing like a wild card in the deck to really complicate things.
That scares the living hell out of me too.
Just keep yourself on as even a keel as you can. Take care of yourself. Don't let your husband throw you out of whack.
I know people have given their opinions on drugs. If you think the medications are necessary, try them. But exhaust as many of the real alternate possibilites as you can first. Exercise, all that stuff. A lot of it actually works, depending on what is causing your problems.
I would never say don't do something that works for you, though. No reason to demonize some chemical help.
