Children's needs (and, where practicable, wants) have to come first while they're dependent. That is not the same as loving them more.
Fortunately, love isn't rationed. Time, money and energy are all finite but love is wonderfully elastic. I didn't love DC2 less because I already had DC1; nor did I stop loving DC1 in order to make room in my heart for DC2 (or 3 or 4!). Likewise I didn't stop loving their father just because I had children to concentrate on. (I don't love or even in the least bit like him now, but that's because he was an arse, not because he was replaced.)
If, heaven forbid, you find yourself having to choose between children and spouse, the answer would usually be to choose the children, but it depends a lot on the circumstances. For example: supposing you married someone who really can't get his/her head round the step-parenting thing and makes the youngsters' lives miserable, he/she would have to go because your first obligation is to your dependent offspring (and would you really want to spend your life with someone who is capable of being horrible to a child?). On the other hand, if they've grown up and left home, then you get together with someone they can't stand, you can jolly well please yourself who you live with. You are not accountable to non-dependent offspring.