Is he happy with his girlfriend?

Is a guy (who is not a sleaze or a player) happy with his girlfriend if he shows interest in someone else? Actually, he is a genuinely nice guy.

Please, no comments about "back off, he has a girlfriend". I am perfectly aware of what is right and what is wrong in this type of situation. I'm just very confused as to why someone who is a good guy would show interest in me, while being in a serious relationship.

Is he happy with his girlfriend?
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