Blended family guilt updated

Crickett★★★
Life is so unbalanced between my two children. I had my 2nd child, a boy, May 15th. My 1st child, also a boy, is 5. I knew things would be different for my oldest with him not being an only child anymore but I didn't think about everything and now I'm feeling guilty. Son #2 was premature and needed 2 weeks in the NICU and being a newborn, he needs more attention than big brother. My oldest hasn't complained so most of the issues are internalized in my own head. My oldest is from a previous marriage and sadly, his dad is a piece crap. His dad also has very little known family living so my family is the entirety of my oldest child's family. My youngest child's father is an amazing person and is happy to be a father. My SO's family is close knit and involved in eachother's lives so my youngest has a lot of people fussing over him. I had trouble bonding with my oldest child as a newborn because of the things I went through during my marriage. I am snuggly and clingy to my 2nd child already. I was so worried when he was in the NICU and went to see him everyday for hours. I just wish things could be better for my oldest. My SO and I give him a good life but I hate that he has a dad who rarely asks to see him and was angry when I was pregnant with him. I grew up being the "other child" I never wanted my kids to go through that and I feel like I failed my oldest and he'll go through it no matter what we do, you can tell by looking my SO is not his dad. Anyone else dealt with feelings like this?
**Update**
It's so weird that I would post this and them receive a call from my ex husband. He wants to sign his parental rights away and my SO wants to adopt my first child. This actually made me happy. I know he's only doing it to avoid child support but my SO adopting my first child really is what is best for him. My SO is Army and going back to active duty. If we have full sole parental rights it makes life so much more smooth.