Just a quick piece of unsolicited advice first: you have some great posters in your thread; don't run them off.
So you asked what else you could do to the extent GAL by itself isn't cutting the amount of head space your ex has. I'm an enormous fan and advocate for mindfulness meditation. I get the sense that you, like me, have an extremely ruminative mind. You chew on and parse over what she writes, you dive deeply into trying to find meaning in any of it, you go back in time and live in those horrible past moments, and you jump forward and worry about moments that haven't happened yet . . . it is a painful, destructive way to live. I'm not judging you -- it was my reality, too.
I don't want to say I don't still ruminate. Once a cud-chewer, always a cud-chewer. But what a mindfulness practice gives you is a rewired brain and, with it, the ability to notice you're ruminating/stressing/worrying/getting lost in your head, etc., break the downward cycle and come back to the moment (where she and your memories and worries can't, and aren't ever going to, hurt you.).
So that's my own personal answer to your "head space" question: start meditating. Today. It will help you, but you have to stick with it. 6-8 weeks from now, probably sooner, you'll realize out of the blue that you just don't get upset or worry or wonder about her texts or, frankly, anything else she does or says to you. You'll see them for what they are: simple pixels on a screen scratched out by an unhappy, unhealthy person you were once in a romantic relationship with whom you now only co-parent.
Status quo isn't working -- nothing to lose. At the very least your blood pressure will come down, and that's even if none of what I'm talking about comes to pass.
Me: 46 W: 44 Married: 17 Together 21 D13; S10 BD: 03.03.15 (Not attracted to you) Almost 2 years trying, alone, to save marriage Status now: Divorced (effective 06.13.17)