No, there are a lot of girls who do the just sex thing too. It's not just a guy thing. I'd say it's more 50/50 rather than it being more guys than girls doing it. I've seen more stories of wives cheating on husbands than I have of husbands cheating on wives (just putthing things into perspective).
I will do my best to reply with an educated, humble and honest answer. Ultimately, it is up to you whether you want to listen to my advice or ignore it completely. Sometimes, my advice may be wrong; occasionally, it will be right. Regardless, I want to do my best to give people answers they are seeking.