My SO and why he's NOT excited for our baby.

Woah! Talk about click bait right? I know, I know. They're everywhere, but the difference in mine is that... there is no lie. No misleading. My fiancé isn't excited for the little life growing inside of me, and frankly, I'm not upset. I'm not mad. I'm reassuring him and telling him everything will be fine.
He was in a relationship for 6 years prior to ours, and has two children with the girl he was with. I adore those two little kids. My world revolves around him and those two, but their mother... she wrecked my fiancé. She kept his children from him for months on end just because she could. I've help him while he cried because he couldn't spend their birthdays with them, because she would vanish with them for months on end. She was mentally absuvie throughout their entire relationship, I've seen the messages, videos, emails, etc. it's not one sided, it's a fact. I have went out of my way to be kind to her and let her know I have no plans on standing between her and my fiancé with their parenting, but as soon as she caught wind I was expecting, she left with the kids (she gets them every weekend, but they live with us.) so we haven't seen or heard from her, or either of them, in almost 2 months.
I'm trying to reassure my fiancé that I AM NOT HER, this is OUR baby. Just because she/he is currently growing in me doesn't give me any more of a right to this child than him, and I will not leave. We honestly have the kind of relationship you see in movies, which most will say is unhealthy because it's "staged and fake" but we just... go. We click. In a way I hope everyone experiences. So, while he isn't excited for reasons not his own, but hers, and what she has put him through, I will continue to reassure, love, and support him. He's terrified I'm going to do what she did and just leave with our baby and he'll never see us again, but I'm not her. I am my own. I am a mother, and I will be a wife. I'm his best friend and he is mine, and this baby is OUR blessing. His just as much as mine. She treats their children like a toy to get him to do as she wishes, but this baby will know unending love from both parents, at once.
He's not excited, and I'm not angry. I love him more for it and being so open with me about it. He, this baby, and his children are my world, and I will continue to prove that for the rest of my life.
Thanks for reading. xxx