Baby mom running my marriage.

So I’ve been married lil over 1 year to my husband. He has a 6 yr old daughter with his ex whom he was with for many years but never married. Ever sense we got together his ex has been a pain. She’s said I’m mean to their daughter, I don’t love his daughter, why did he marry me, why is he having a kid with me ( I’m 7 months pregnant). She goes on and on constantly belittling me to him. She says we only have fancy stuff n it won’t last, constantly text him that she hungry or bored n talks like they are still together. My husband won’t put a stop to it and gets mad if I say anything. This morning I saw a bunch more text messages in his phone from her. She’s basically saying it’s Valentine’s Day Friday he needs to take his daughter and not take me anywhere on Valentine’s Day his daughter comes first. Mind you a year and a half ago she wouldn’t let him see his daughter, she uses her to get to him. She’s been in other relationships but as soon as they fail she starts bothering him again. But when she’s in these relationships she ignores him blocks him doesn’t want anything to do with him. Well she is single again and starting her stuff and I feel that it is over for me and my husband. I can’t take it anymore. I’m pregnant so obviously don’t want to get a divorce before my baby is here nor be a single mom again. But I can’t allow them to talk behind my back and the constant disrespect or accusations I’m “mean” to their child. I’m about to give up! I’ve never talked to his ex once. I never stick up for myself but I’m going to start n it’s going to end my marriage leaving her with what she wanted. Him back with her n me and our new baby gone :( How do I get her to move on and him to respect me as his wife to let her go?! Or do I just leave!? So sad :(