I don't get this topic sir.
Nobody else here will be able to tell you what turns YOU on, we can only tell you what turns us on, and what we've heard turns other people on.
Take your time, think about what catches your eye, or your penis for that matter. Go through some various porn themes, see when you feel the most aroused, etc.
It seems your gf does like you enough to want to make you aroused, she sounds like somebody who is willing to experiment. Have her try a range of things on you and see what gets your boat rocking. Simple kissing, light touches, strip teasing, masturbating in front of you, wearing a school girl outfit, talking dirty and spanking you, tickling your feet, etc, who knows! Not us, only you will find out.