I haven't gone from one to two children but maybe you feel like you have to distance yourself from him bc he's not a baby anymore/ doesn't depend on you like the infant does.

Or maybe a past problem? I distanced myself from my only son when he was about 8-9 years old.. Distance myself before he could pull away and hurt me first (I was around 7/8 when my mom seemed to have pulled away so I felt it was natural for the mom to do it)... it took A LOT of effort to regain that bond we (son and I) once had.

Or maybe you're just plain out exhausted? You have to experience new baby's stuff, so once the oldest comes around, you don't have the mental capacity to function for him. I know baby is still really, really young but could dad watch her so you can nap and then plan a special mother/ son date, even if it's to the park and ice cream for an hour. Just taking some time strictly for you two.

Another option, PPD? Hormones are still wonky. The good thing is that you realize your emotions, you want better and you've reached out (to reddit but it's still something).