Am I right to feel p****d off?

Me and my partner are expecting a baby. Therefore his child maintenance payments to his ex girlfriend will be reduced by £28 a month because of our little one. He already pays her a hefty lot because he earns quite a bit (irrelevant but needed for you guys to understand where I'm coming from). He just said to me he's not changing the payments so we'll be £28 better off a month because, "he wants to keep the peace" with his ex. This has wound me right up! I understand keeping the peace but this is just beyond, I feel like my baby is going to be 2nd best 😢