His daughter with another woman vs our daughter

My hubby has a 4yr old from a 1 night stand(yes,this can happen!). I love her. Ive been around her since she was 1.5yr old. We now just had a daughter of our own and things are how I worried they would be.

I feel like he loves his 1st daughter so much. Like more than ours. And I do know he loves ours,but its just so different.

Im aware that us having her half the time,I think my hubby has to make up for their time,since we dont see his daughter every day. Im trying to get this through my head.

Is your 1st kid just always secretly number one? I dont know how that is yet, since I just have 1 biological daughter. I am also still very hormonal after birth, so maybe im just being over sensitive.

Does anyone know what Im going thru? I just want him to give the same attention to his 4yr old to our baby. Nobody is more important,I just want fairness 😕