Any advice on managing discussions with a partner?

We are both ADHD and maybe he's an Aspie, so it's really hard for us to stay calm and not react impulsively. We both know the theory and some grounding technique, but when we argue we forget completely and just cannot avoid saying things we know we shouldn't. We both fear each other abandonment and rejection so every time one of us says something inappropriate we end up in this resentment tunnel and need days to reconnect. Please help if you found a way to keep calm, this is so draining ☹️