Husband rant!!! Stepchild follow up!!!

I just posted about my nightmare stepchild yesterday. I decided to have a conversation with my SO when he returned from work and had adequate time to relax and settle in. His immediately became defensive and said he picked my side over his sons repeatedly and he picked the "right side." This made me so angry for some reason. Then he said if I don't want his son to hurt the baby I should spend more time with him like Jen and Devon (ex girlfriends) because I am stand offish with him and from a 10 year olds mind you would target the one who gives you less attention. I am so furious and I can't calm myself down. I want to have a break up conversation but I don't know if I'm being overly hormonal I am just so baffled, hurt, and angry.