Hey. I'm Not sure exactly what you are looking for here. You already know it is a bad idea. Nobody on a support forum is going to say that yes you should cheat on your husband, so I am going to guess that you posted this looking for someone to talk you out of it?? If so- Don't do it!

I Dont know if this is illness or medication related. Maybe. Hypomania can cause hypersexuality, Some medications can kill sex drive. But an Unsatisfying relationship can also cause people to look for it elsewhere, and that has nothing to do with having an illness.

I'm sorry you are not getting the affection you need or deserve from your husband. That sucks. But hooking up with a stranger is risky and can have some pretty big possible consequences. And In my opinion, a random hookup with a stranger isn't even usually very good sex. I cheated on a boyfriend once and even while it was happening I already hated myself. Not worth it.

Whatever you decide- Be safe.
If you think this is a symptom and your thinking and mood is heading into dangerous territory,, call your pdoc or therapist asap. Best of luck.