If a man cheats on his wife does it mean he s not happy?

No it means he's greedy

Maybe.

Maybe it means he just doesn't respect his wife (at least not enough to remain faithful).

Not all people who cheat are unhappy in their relationship. Sometimes they cheat just because the opportunity presents itself or because they want something different (sexually), but are otherwise happy/content in their primary relationship.

Saying they must be unhappy if they cheated is an attempt to excuse the behavior, but it doesn't work that way. Even unhappiness isn't a good excuse/reason, but the fact is that a large portion of cheaters aren't unhappy with their spouse when they cheat.

It means he is a selfish sociopath who doesn't love or respect her. She should leave him and take him for everything he has in court.

it can mean exactly that or it can just mean that the cheating is a form escapism from boredom ,its the same for men and women.

Correct

No he cheats because he WANTS to cheat.

It means he lacks self respect and may not be marriage material. It means he is not happy with himself and needs to get it right with God.

It means he's a scumbag.

no-he's happy...
getting the hottest a... he can

That seems a reasonable conclusion. There is no question that a cheater cheats because s/he is missing something in her/his marriage that s/he feels s/he can find with someone other than her/his spouse.

I think it's more complicated than happiness. I've never been married but I have cheated on a few long term partners. Sometimes it the thrill of just doing it, sometimes it's a once in a lifetime opportunity, maybe it was just too easy to pass up. I will say that I think it's a sign that you no longer love the person you've cheated on. You can be happy with someone and not in love with them. You can be unhappy with someone and still love them. Happy is not a long term emotion, it is short lived.

Yes, something is missing in the relationship.