Lies aren't always the answer
It's possible that you may not be comfortable with all this sincerity. If it's your intention to lie about the true nature of your evening, do so very cautiously. A wise man once said that when two people know a secret, it's no longer a secret.
With other guys involved, lies have a very good chance of catching up with you. Your buddy may have a tolerant girlfriend who won't mind hearing about the depravity. But watch your back if she shoots her mouth off to your spouse, especially if she's not so broadminded. Don't be reckless; evaluate your chances first.
Keep in mind that talk is cheap and a woman is likely to judge your actions. If she's used to seeing you acting crudely and lewdly toward women or constantly eyeballing the all-night buffet, so to speak, don't be surprised if she goes completely ballistic when you suggest that you might be going out with the boys. Earn her trust and I guarantee she won't give you trouble over the next boys' night out.