What side effects/symptoms are you having? I HIGHLY doubt its from your fiance taking antidepressents.
I suppose that theroy may (and this is a BIG may) be plausable, but I find it highly unlikly.
At least there is absolutly no medical evedence to indicate this as a possiblility.
I suppose you could conduct your own experiment and use a condom for a couple months to see if the effects go away.