Of course you care what STBX does. His actions affect the kids. But they are HIS actions and HIS choices to make. Trying to control his actions and his R with the kids is not going to help the kids.
Texting and email work fine for reporting basic information: "S is angry and does not want to visit." That is useful info for STBX to have when he sees son.
It is when you try to do more than that that you get frustrated with the communication. Let go of trying to control STBX's R with the kids. Sadly, they are going to have to adjust and you are going to have to accept that you can't do that for them.
Consider that right now by wanting to indulge your son you risk coming between him and his father. You risk creating a dynamic in which you are right and STBX is wrong. You look to be supporting a view of the situation in which you are the victim and his father is the bad guy. You are putting your son in a position in which to love you properly he has to reject his father. Son darn well knows you like it when he says things against his father's actions and against the GF. Indulging him by trying to keep him from his father reinforces that for him, and proves further to him that he really does need to be anti-them to be pro-you. If you really want what is best for your son, don't let him be in the middle of this crap in this way.
Visitation and custody schedules shouldn't be his choice (and aren't legally). It shouldn't even be something that he feels is on the table. He doesn't need the stress and burden of trying to figure out how to manage that choice while still loving his father and supporting you.
If you really want C to be successful for the kids, don't try to force it on STBX. Let the kids go to the C. Text STBX a simple report: "FYI, kids have C appointment on Tuesday at 9 with Dr. Cathy, phone, 555-5555." Let the C handle making recommendations about whether you or their father should join them. Stay out of managing STBX's side of things.
And if you really want to help your kids, then help them feel it is OK to love you and STBX both without judgment. Tell them it is OK for them to love their father. Tell them it is OK for them to like, even love, his GF. Tell them you know they have enough love for everyone and you want them to have a great R with their dad.
