If you want ideas, here's my absolute 100% favorite sex thing in the world (if she's into a bit of humiliation). More domination than bondage, but there's some tying up and pinning involved:

You tie her hands really tight behind her back, and you have your way with her. You fuck her, you make her suck your cock. If she complains that she's drooling you say "good", and force your cock deep down her throat again. (Every once in a while checking that she's actually ok with it.)

Then you turn her around and start fucking her hard from behind while rubbing her clit... as she starts getting close to cumming, you stop and pull her by the hair and say "Slut, you don't get to cum until you make me cum". -- Maybe go down on her for a bit, then as she gets close you slap her in the face: "Slut, I told you you don't get to cum until you make me cum." -- You do this a few times until she's really worked up, and you're ready to fucking explode.

You make her work hard. By this point she's a sweaty, drooling mess. And you finally grab her by the hair, tell her to show you her tongue, maybe hold her by the mouth, and you cover her face in your cum. You can't believe you had so much cum inside you as it keeps gushing out. At this point she's so worked up, you won't believe with how much gusto she'll rub her face all over your cum. It's the most beautiful sight in the world. You can see and smell yourself on her. She's your plaything.

Now you tell her if she wants to cum, she's gonna have to beg for it. And she will. So you go down on her (she's still tied up), her pussy is on fucking fire by this point.

As you look up, you will see her writhing, your cum dripping down her face. She is tasting, smelling, feeling you all over her as you pleasure her. You let her know what a beautiful fucking mess she looks like right now. What would her friends think if they knew what a dirty cum slut she is? -- Finally you make her cum with your fingers and your tongue at the same time. -- I have never felt my girl cum so hard as when we do this. You make her cum over and over until she can't take it any more (there's nothing she can do about it -- hold her legs / torso down if you must).

And when she can't, just when she thinks it's all over, you tell her "I'm not done with you yet". And you gag her and fuck her even harder from behind, holding her by the gag tied around her mouth, your cum still dripping down her face, and finally you cum a second time inside her (or on her face again).

Then you both sleep like babies.