I don't understand why any guy would deny his wife the sexual pleasure she desires, even if it involves her getting that pleasure from a dildo.
If she desires something bigger than what you have to offer. To my way of thinking all the guy is doing is pushing her into another man's waiting arms. Let her have her dildo and help her experience that pleasure with you, It might well be the thing she needs and prevent her cheating to get the real thing. Guy's just get over the ego trip and look after he sexually or someone else will likely do it for you.