Replying to Whats up with girls?

What the hell is up with girls do they have some freaky radar telling them that guys have a girlfriend or something?

I have a bunch of friends who are girls and never seemed interested in me and last week I started going out with this girl and now alot of the earlier girls are starting to seem interested in me like they flirt with me and compliment me and look at me with a look that I recognize as "I am atracted to you"

non of them know I have a girlfriend because they dont know her and i havnt told them about her. this behavior started around the same time I started going out with this girl.

so girls spill the beans how is this happening. I heard the same thing happens to married guys girls start getting into them.