Push her away. @albert_camus is right, you're going to hurt them either way, but it's easier to forget someone whom you have less memories off. Think of it like ripping a bandaid off. You wanna do it slowly or quickly?
Let me add though, I mean, if you're solid in your CTB, and you feel you're solid in your decision.. will it affect the method? if not, i mean. youre going to hurt her anyway, might as well leave some good memories.
I don't think pushing her away will necessarily make it better. Good memories with you are probably a good thing, but as I already said: u will hurt her. So of course you should think about it twice or probably more than twice.
The only reason I'm still here are my loved ones. Sometimes I think it would be better for them if I ctb, but tbh, we all know the truth. Killing yourself is one of the worst things you could to do to your loved ones, even if your brain tells you otherwise. In my environment I see what it does to them if loved ones kill themselves. My sister did the same and years later, my Dad still blames it on him.
I don't want you to feel bad, but I think people need to know what it means for those who stay on these fucked up world, you know.
Suicide isn't selfish, but it will hurt so many people, even if they understand why you did it. I would say suicide isn't a good thing in any case except you would turn into a mass murderer or something if you wouldn't ctb instead. I hope this makes sense. Sooner or later we'll die anyway.