I don't know if the writers will touch on it in season 4 BUT
There's something about Yasammy that I haven't seen many people point in, in that both of them put the other on such a pedestal that when real life happened, it really added to the communication issues in their relationship.
Sammy has always been Yaz's number one cheerleader; she's always been convinced Yaz can do anything, until her PTSD. Yaz struggles with her PTSD for about 2 years before Brooklyn gets her into Dino Immersion Therapy, 14 months before the Chaos Theory Events. Yaz for 2 years wasn't the person Sammy built her up to be because everything was affected by her PTSD, and Sammy's decision to protect her could easily be seen as Sammy not believing Yaz can get better; suddenly, Yaz isn't the person Sammy always praised her of being. Even in her Flashback with Brooklynn, Yaz says she thinks the therapy would be good for "us" meaning her and Sammy. She thought of Sammy when she was deciding to go to Wyoming, it wasn't a selfish one-sided decision, she wanted to be a better person FOR SAMMY.
Then on the flip side, Yaz is always praising Sammy's strength, but then she leaves, and Sammy is alone and she's not dealing with being alone well and of course this isn't communicated to Yaz who thinks her girlfriend is fine because It's Sammy she's country strong and surely she's good because she hasn't told Yaz she's not and Yaz wouldn't suspect anything because her girlfriend can do anything, she's a strong woman who runs her own ranch. But Sammy's not as strong as Yaz's perception claims she is, thus more communication issues.
The thing of it is, they have to accept each other at their messiest. They have to believe in each other enough to know that they don't need to meet each other's expectations of the other all the time and that they can rely on each other even when they're hurting.
They don't have to be perfect for the other, they can be hurting or upset or angry or messy, and the other WILL STILL LOVE THEM FOR IT. That's the lesson both of them are missing. They need to know they can be weak with the other, they can be less than ideal, and the other person won't see them as less because of it.