I never knew that tattoo parlors were open well into the night but I hope it doesn't always keep you awake and occupied for that long. But with what you have in your profile, me thinks that you've got your work cut out for you. :)
I wish I was any good at drawing. I was contemplating getting a tattoo but the sketch looks meh; and I am working on something with a friend but it requires a map and the map is also not the best (although I guess it could be worse).

Gabriel will probably be a little more open to certain aspects of bondage, discipline, domination and submission as their relationship progresses, but he will also have good reason to react violently to her trying to push him on practices that involve pain or gags, among other things. 
Likewise, he might find himself interested in the domination aspects of BDSM and in putting Nadine in a role she might not usually fulfill, though it would also remain to be seen how she would react to that.
At the end of the day, I believe that, going by what you wrote, Nadine and Gabriel both want stability, trust, a bit of tenderness and, of course, great sex in their life, so they have something to work with while they explore this side of each other and find out more about magic, and by the time they may become frustrated about certain things being touchy or off-limits, they have alternatives.