Another two things to consider
1. If you haven't had the snip, what happens if she gets pregnant? There's always this risk in any sexual relationship that involves non 100% reliable contraception. What happens then? Would you enjoy having an open relationship with her if she has your baby (or some other guy's) or would it totally screw your head up? Also, what happens if she picks something up off one of the hot guys she brings back or shags elsewhere? Casual sex can be fun for a while (it was for me), but the more you do it, the more risks you take. Most of the people I know in long-term open relationships have herpes, chlamydia or similar infections.

2. If you haven't been constantly going on to her in a bantery way about all the hot girls you've seen lately, why should she suddenly bring pulling hot men up in conversation and assume you'd want to talk that way? Strikes me as a tad odd and presumptuous. Unless she's mad or totally lacking in social skills, it sounds like she was doing it deliberately, to hurt you and get a reaction.
(IHateSprouts is baking a huge pie shaped like an enormous pie, Wed 12 Jan 2011, 19:27, Reply)