am I a bad person??

I’ve been with my boyfriend for a year now, but he already has a daughter who is two. Him & his baby mom are on decent terms, she is in a new relationship as well and him and I have been talking about kids... We got pregnant at the beginning of our relationship but I miscarried very early, it’s a year later and he wants to start trying soon as he wants more kids and I want them too... here’s my thing... idk how I feel about having a baby with somebody who already has one.. I feel like I’ll never get the “firsts” and it won’t be special to him. I’ll constantly feel like he’s thinking about his ex. I love his daughter with my whole heart, but I can’t help but feel bothered by this... am I wrong? Idk how to move past it. Idk what to do. I don’t want to leave him bc he already has a baby but I’m just scared. Somebody please give me any advice. I don’t really have friends to talk about this with.