Is it wrong that I want to pleasure myself instead of having sex with my girlfriend?
Would you like to try it out?
Some other time, sometimes I get a little bit too horny around her
There is nothing wrong with that. I am sure your gf won't mind and might join you.
She's afraid to have sex with me cus I'll hate her.
It's fine to pleasure yourself if you and your girlfriend are not having sex. This can stop you from being irritable if you are too desperate for sex.