Dump her.
Right now she's the dominant partner and when you simply say "You know what, we are done. Best of luck but I'm out." and leave the room she will be fucking stunned.
You'll feel like King Shit for it too. Just say the words and leave. When she messages, and she will, you get to reply one time: I realized that this wasn't good for me and needed to end. It's over. I've got nothing else to say.
Then don't respond anymore. Mute her even. Let the messages stack up but don't look and don't reply.
Go have fun, do things, date others without expecting them to be 'the one' and enjoy the time.
Then in about a month or so (2017 mofo) view her messages and say "Hey, I'm sorry but I needed space at the time. Couldn't read. Couldn't reply. I hope you are well."
She'll see this as her chance and engage positively. For a bit just reply some and wander away. No more than three lines.
Then, around valentines or st. patty's flirt with her. "You know I always liked your smile. I know we can't be together but you are still cute." etc.
Again, keep the converstation minimal. Never respond immediatley. When you do, say a few things, including a compliment every now and then, and then move on.
Continue to date others, for fun. Just fun. No stressing about it. Talk to your ex casually about it. "Sorry I didn't see this and respond last night. Was on a date. How's your dating going?" make like it's no big deal.
At first she'll want your revenge, but then seeing you so happy she'll be desperate to get back with you for long enough to dump you. Just to prove she's still got it.
Feed this slowly and by next summer you can FWB her without the relationship.
Wear condoms. No babies you dipshit.
