I've been through few prompts here, and I appreciate how many people have tried to find a way to play with me in this. After some work, I think I've refined the prompt that I really want, and then we'll see if anyone wants to play along.
I'm your girlfriend, totally devoted to you. You are the most important thing in my life -- pleasing you is the only thing that really matters to me. It's not a spelled out Ds relationship, but I'm so desperate to keep you that I'll do anything.
But you're bored. I'm pretty enough (5-6, 135, brown hair, B cup), but I don't bring a lot of your life other than having someone who is dedicated to pleasing you. You've met someone new, and she's a little cruel, a little manipulative. And she pitches you an idea -- what if you made me into her dog's girlfriend? Eventually breaking me to the point where I become his full-time mate to the amusement of you and your new lover.
Just a few ground rules. I don't like costumes or suits, so if that's a big part of your kink we won't be compatible. I'd prefer if it you take sex with you off the table as soon as possible. And a little bit of contempt is always fun. And I'd like your goal to make me as much of a dog as you can, and make me want to be your or her dog's girlfriend.
DM or chat is fine. I usually can play during the weekdays US Mountain time (GM 7) but then I have to go home to my usual life and roommates and such. If all of that sounds fun, drop me a line.