If your comments about girls on the street were only a few months ago, she could easily have been harboring hurt about that all this time. Were you noticing the insecurity before that?
I know the other responses you've gotten have been pretty much of the, "she's messed up, drop her," type, but you sound like you're surprised by her new insecurity, and care enough to want to understand, not just drop her.
It is hard (I don't care what the big strong people say
) to hear a boyfriend comment on other girls. No one thinks you can not notice a pretty girl, but you don't need to tell your girlfriend. That was a mistake. And she could still be hurt about it.
I can hear the big strong people again-- "She shouldn't still be hurting over that! Of course he looks at other girls! What does she expect, him to not notice pretty girls?" But there's a difference between realizing that, naturally, your boyfriend notices other girls, and actually having to hear about it. Some people get their feelings hurt by things like that, and some people don't.
So maybe you need to ask yourself, 1. Is the insecurity really a new problem, and can I help her with it? and 2. If it's not really new and she's just a more insecure person (some of us are
), then do you accept that as just one of the imperfections you deal with in a relationship, or is it unacceptable to you?
Also, does she (don't answer this here, I'm just suggesting you answer this honestly in your own mind) have some reason to wonder if you're watching the "other" channels? It sort of seems like that would be based on something, so maybe consider if these trust issues are based on anything that's happened before...