My stepson is making my marriage miserable

First time writing here, but I just have to talk abou it with someone. I'm now pregnant with my second child with my husband and I think his son would be our breaking point. I have a son from another marriage and my stepson loves to bully him, but it's not like the typical kids bullying. His behavior is to the extreme. He talks to my son like shit when no one is around and he does the samething when his dad isn't around. The kid is a two face in front certain people he wants them to believe, he is an angel but in really he is pure evil. Last night, I caught him talking to my son like shit so I addressed it and told him if he would like to someone older than him to treat that way. While I was addressing the issue he looked at me like he wanted to hit me. So I furiously told my husband and like always he to his side. My husband think his child is not capable of doing any wrong, he could have the evidence in front of his face and he acts in the denial. Long story short, I almost ended up at the hospital because the situation elevated my blood pressure. Still my husband didn't care to asked if I was doing better, like everything he ignores everything. His son's behavior have been something that even his parents pointed out, but when I bring it up my husband goes again into denial and says that no one complains about his son which is be lie. He loves to say he is just a kid, the kid is 12 year old at that age they sure know what they are doing and why they do it. They make seeing like I am the problem, but I'm sure I am not because I had 4 stepkids at once from my previous marriage and I never had a single problem with them. Until this day, they are respectful to me. I think that difference is that my ex raised his with discipline and wasn't blind, he made sure they respected me always. I don't know how much longer I could take it, but I'm starting to resent my husband for it even more after he told me in front of his kid that the kid is going to hate me. He forgets he has one child with me and another one on the way. He acts like his son is the only person he has to care for. During my last pregnancy, I spent it alone because he left the house due to his son. I'm sure that if I give him an ultimatum of either decipline and make him respect me or leave he would leave me in heart beat. His actions have shown me that he really doesn't love me like he says he does because at this point, he would've made some changes and at least act like he cares.