I'm secretly jealous of my gf
Are you serious? Why would you be jealous of your own girlfriend?
She's very feminine, and I would have liked it if she were a bit more masculine.
There's no real reason for you to be jealous of your girlfriend, if you're in a healthy relationship with her then you should be able to accept who both you and she are. If you would like to be more feminine like her then you should tell her and do what you want to do, and if she is a good girlfriend then she'll support you.
I just would prefer for her to not be so feminine. Masculinity is much more attractive.
Okay, so this is not some thing you should be jealous of. talk to her and tell her how you feel.