my boyfriends new baby with ex

sooo long story short, my boyfriend and i got together back in december and he had just got out of a relationship shortly before we got together, so turns out his ex was pregnant and the whole time we been together she has been pretty quiet and to herself and we figured that it was because she was lying its being pregnant since she has done so in the past buttt unfortunately that was not the case, she just had the baby about a month and a half ago and my boyfriend wasent there for the birth or anything but he is now in the child’s life. so i guess i just want advice on how to support him without seeming i guess salty lolll , it’s really hard for me because i really wanted to be the one to have his first baby and now that’s not going to happen and it makes me sad because i really want a baby with him and idk i just feel weird. like when he talks about the baby i try really hard to sound happy for him but it’s just so hard when you think about the whole situation and how things are. i understand the child is not going anywhere and i understand the baby didn’t do anything, i have no negative anything towards the baby. the baby’s mom, yes because she’s immature and very childish but that’s about it. how can i deal with this?