I would, however, tell her about herself. Say, look, I wouldn't be with you if I didn't care for you, and you need to get on board with that. There are other women around, yes, but I'm clearly not with them and don't plan to be, so get the hell out of my face about it. If you can't, then you don't trust me, and we have a bigger issue we should be discussing.

It's hugely insulting (imo) to be constantly challenged about fidelity and honesty. I think it's important that you express that to her. You don't have to be an ass about it, but you do have to stand up for yourself if you want a strong relationship... and if the relationship won't stand up to that, maybe it isn't the right one for you.