You may not want to hear it, but you need to get out of that relationship. PTSD or not, he is putting you and, most importantly, your child in serious danger. I hope you are gone to your mother's before he gets him. I'd hate for him to have the opportunity to stop you.
As to your recovery, you're never going to get clean in the situation you are in. Do you really think that the answer is just to take an extra dose of suboxone when this happens and then cut back the next day? Pretty soon you'll be taking an extra dose every time you get stressed. I am a huge proponent of suboxone and have seen it work wonders, myself included, but that's not how it works. It will give you a chance to address your problems and using and that is great. But when you get stressed and take more than you are prescribed, you are engaging in exactly the behavior that got you where you are.
I really hope you don't take me as too harsh, but you need to get out of that situation if you want a realistic shot at sobriety. I'm pulling for you (and your kid)