I agree with these guys.
There is absolutely no reason, other than selfish insecurity, for your husband to get two pussies when you only get one cock. You and the girlfriend are not a harem, and he is not a sultan. So why should you be treated that way?
My thoughts on this are to confront him and lay it down. If he gets to have a girlfriend, then you get to have a boyfriend. If you're only allowed one cock, then he's only allowed one pussy. Because you said, the double-standard bothers you. And you have every right to be bothered by that. Women have fought really hard over the past 40 years to gain equality, and we don't need pigs like this screwing that up