I guess the question is what are your concerns?
Does the nature of relationship you wish to build require exclusivity? If so, why? Are you afraid of disease, uncertain paternity, embarrassed for others to find out your love is non-traditional, or looking to feel a sense of leadership or ownership in the relationship which might be challenged by another partner?
I am not saying any of those are wrong. But identifying what your exact concerns are could be a good way to self examine if this is a deal breaker or something you can live with.
At the end of the day, relationships are deeply personal. You are not less of a man if you date a polyamorous woman, so long as everyone involved is able to give informed consent. Neither are you a bad person if you feel that you require monogamy to be happy in a relationship.
You have to make sure that things can work for you. And then you make sure things can work for her. If you cannot come to terms, you can part amicably on the understanding that your lives have different paths.