Why are some guys very tolerant of girlfriend that cheat on them repeatedly?

This simple guy in my office has been dating a hot model. She has already turned down his proposal twice. Three times she has had one night stand with rich men. Heavens knows how many other boyfriend she has. She moves around in midriff baring dress. Any guy will love to date someone this hot but what if she is always sleeping around? Don't some guys have any sense of self respect?
Why are some guys very tolerant of girlfriend that cheat on them repeatedly?
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