Its not a girl or guy thing, some people just have no decency or compassion and toy with other peoples feelings to get what they want. Luckily scum attracts scum, so when this girl does find that dream boat guy, she might find herself to be the temporary girl aka one night stand.
Well, maybe some girls would date other guys if they're lonely, whether they realize it or not.
Some girls might want to get someone jealous or something.
But personally, I wouldn't start any relationship with anyone I haven't liked and known for a long time.