I'm thinking he was smiling because he didn't form a prenup with Jade and this may have been his way out of the marriage without losing half his assets.
We know he didn't sign a prenup with Jade as she brings that up when the mc was fucking her while she was arguing with Burke through the door.
Jade: "No! If you get the screwdriver, you can bring the divorce papers with it!"
Burke: "Will you stop threatening me with that! We're not getting divorced!"
Jade: "Only because you were stupid to not get a prenup, you jackass!"
That exchange tells us that Burke brought the money into the marriage. So not getting a prenup contract means if they divorce she'll get half.
Now while it's no longer relevant in some US states, there are other states where you can file for a "Fault Divorce" which can lead to a reduction in the distribution of the marital property to the party that was at fault (depending on the state).
Now sure, we and Jade know Burke's also been unfaithful, he even admitted it to her, but she has no proof. But he does have proof.
So the next time she threatens for divorce, he'll be like:
Burke: "Sure bitch, let's get the papers now."
Jade: "I'll take half you know, you wouldn't dare!"
Burke: "This video of you screwing Fuckface says otherwise!"
Jade: "
!"
So he's basically got her over a barrel.