Need help in staying calm with aggression

So P has been having increasing bouts of aggression towards me and I have been unable to remain calm-instead I'm feeding into her ramping up. Last weekend, I hit her back after she pinched me while driving then wouldn't let me get the baby out of the back seat. The CW found out because I called for respite and P yelled into the phone "she slapped me." I wouldn't have lied anyway, but after all was said and done, I just needed to re-sign a safety plan and begin family therapy with, yet another therapist. I don't know if its the upcoming adoption, the jealousy of when I need to care for the baby, or what, but I am starting to lose my patience. Anyone have a good resource out there to help me maintain my cool?