First time for me, not my husband

My husband has two girls with another woman, they’re 11 and 12. My husband was never married to this woman and it wasn’t the best relationship in any way. I am almost 16 weeks pregnant and I’m very happy, I had wanted this with him for a very long time but now I’m starting to feel depressed and disappointed. I’m also sad that it’s a girl but only because he already has girls, while he doesn’t show it, I know he would’ve been thrilled to have a boy, at least that would’ve been a first for something in this pregnancy... this woman is very toxic, she’s malicious, she’s vindictive, she’s just a nasty woman which is making everything even harder on me. For those of you who have had your first but not your husbands, how has it changed your family dynamics or your marriage? I feel very protective, imagine a toddler saying “mine, mine, mine” that’s me right now with my sweet girl. it has been very hard to not want to hate my husband, I have been purposefully picking fights, I do not want to be this way but it’s so hard. It’s hard to not feel sad and like something has been taken from me. I didn’t know being a step mom and being in a blended family would be this hard, if I would’ve known, I might not have been with him but I love my husband more than anything, so don’t get me wrong.