Are your girlfriends free to have sex with other men?

It isn't the case for my regular current girlfriends.

I have had friendship with benefits relationships where this is the case. I certainly considered the women involved my friends, not really girlfriends however. Also in those I didn't experiment with traditionalist patriarchal mindsets.

Do you value having sex with girls with whom you don't want to start families?

Not really. I elaborated on how I view it a few years ago.