Age Gaps? ADVICE PLEASE!

Jessica
I have a 5 year old son and I'm 37+1 with a girl, my son goes from "I hate babies" to "I want a brother" to "I'll share my toys and feed her and cuddle her" so it all depends on the day as to how he feels. Just wondering what everyone's experiences are with adjusting a child that has always had all of mummys attention to needing to share. He's incredibly clingy to me which I've always loved but now I'm a little worried he'll resent her and it won't go well. Also a little worried about them getting along since there's a 5 year age gap. Any advice?