I totally understand, this guilt is something I feel like I face everyday. I try to make up for it while my youngest naps or I lay back with my baby on my chest to nurse so I have both hands free to use toys to play pretend or sing songs. I’m slowly finding little ways to connect with both solo but man the guilt is real, you’re not alone 💓
I invite big brother to cuddle with us, it's the only time I let my 17 month old watch TV. If he doesn't want cuddles and TV I try to give parallel talk ashe plays on the floor so he knows I'm still seeing him and like what he's doing. Worse case senerio I just offer a repairing hug and play time after sister falls asleep even if it's just for a little while