Your fiancee did the right thing. Going from totally flat to totally pumped my arms go from maybe 18" to 18.75" if that. And no way you put on 1/2" or 3/4" to your arms since measured. All my suits are custom made. I'm talking picking out a roll of fabric and a style from a catalogue. Three quarters of an inch is FAR too off for a $2300 suit. I would freak. And I have half a dozen suits and probably 8 or 10 sport coats all custom. They get a little snug or a little loose through all my ups and downs just under 6', 220-260lbs. But always still wearable.
Everyone saying diet off size or flatten out, or adjust PEDs to make a fit, that's just silly.
Oh, and congratulations BTW. Enjoy your big day. (and the honeymoon even more)