Most Helpful Girl
Treat her how you'd treat a wife and one day she might become yours.
That's the advice my boyfriend's dad gave him when they first accepted his dating me.
You have to be supportive of her and her interests. That doesn't mean you suddenly have to like all the things she likes, but you have to support her liking them.
Be respectful. She's not your toy. She's not something you get to flaunt around and dangle in front of your guy friends.
She's not an automatic lay for you. So don't act like you're entitled to sleep with her. You're not.
Be honest with her. Don't cheat. And if you think you want to cheat then do her the honor of breaking up with her first. In the long run you'll both thank you for that.
Most Helpful Guy
Try not to fuck up