Sick and tired of being a stepmom

Since I've gotten pregnant, I've started feeling like I can't stand my 3 yr old SD. She's severely attached to her father and I'm pregnant with his second baby. I guess it all started when he found out I was pregnant and doesn't show any affection towards the belly at all. He acts like he doesn't really care or isn't as excited at all about this new baby.

Since then, whenever I see him smooching on his daughter or cuddling with her, it makes me resent her and him. Sometimes I wish she wasn't in the picture at all. I even Hate him for having a child with someone else sometimes. I feel like he loves her more than our baby.

Sad part about it is, before he acted this way with my pregnancy, I was in love with his daughter. Treated her like my own, and I still take care of her 24/7. Some days I love her, some days I resent her. How can I get back to loving her like my own? I hate that I feel this way over a toddler. I know it's not her fault but I can't help how I feel. Advice???