@mnuser2021 I have read all of your posts on this thread, but not all of the others, so apologies if I say what has already been said.
I am straight, but I think I love you OP. In some ways your post is very sad in that you feel that you cannot love your DSS in the same way, or as much as your DC. But OP, your OP is absolutely full of love for your DSS. If you didn't have any biological children of your own - for whatever reason - you might wonder about it (as you are obviously both a very thoughtful and intelligent person), but you wouldn't know for sure whether you would love your own biological child more, or maybe how much more than your DSC.
I think that particularly when our children are still actually children, rather than being adults, it would be almost inevitable for us to love our own children that bit more, especially when their bio mum is still on the scene. However in my experience (and I am the only person whose experience I can talk about!) when I became pregnant with my second child I was really worried about whether/how I could possibly love my second child as much as my first child, because I already loved my first child so very much.
When my second child was born I fell in love with them as soon as they were born - I had of course loved them when they were still in my womb, and would have been devastated if I had lost them while pregnant, but I was still worried in case it wasn't as much as my first (PFB) - My second child is the same sex as my first, so I don't know if they had they been the other sex, whether that would make any difference, but in my case I don't think it would have. I later went on to have a third child (same sex again, and still not a problem). My second baby had, and still does have, a very different temperament to my first child, and then my third had, and has, a very different character to the other two!
I actually found bringing up two young children easier than when I just had one, but that was probably because I had already learned so much baby related with baby number one - I had virtually no experience at all with babies until I had my first - when I was about 9 I pushed a baby in it's pram for about 10 minutes, and when I was about 14 or 15 I held a 6 month old baby on my knee for about a minute, but she started crying so I gave her back to her mum almost straight away 🙈 That was the sum knowledge of babies until I had my own.
Anyway, the point I am trying to make above, is that your baby is your first born, and obviously I have no idea how much experience you already had with newborns, but if not much, you might find having a second baby much easier than having one baby, and one older stepchild. So if you want another bio child please don't rule it out because of your recent experience. Your DSS will also have experience now of being an older sibling.
@mnuser2021 I felt (and still feel now even though I am now a grandmother) a different love with all of my children. I don't mean that I love one more than either of the other two, and I can't think of a way of describing my love for each of them - even to myself - but every baby became the most vunerable of my children when they were born, and that was simply because a tiny baby is more vunerable than most older children, so if there was a fire in the house most of us would try to dave the baby first as it couldn't climb or run away from the danger by itself.
I am not trying to suggest that that is why you feel differently towards your two children, as I think it is only human nature to do so in your sort of situation, but with one of your children being so young, your different feelings might be for more complex reasons than just one being your stepchild and one being your born to you child.
By the way when my husband and I only had our youngest child at home, while the other two were with their Grandparents, we used to enjoy it being just the three of us, and having a rest from the other two.
You are such a lovely mum, stepmum, and person, that I think you need to try to stop thinking about the negatives of a situation that you can't change without making such drastic changes that I think you would hate them, and that would not make you happy, even in the long run. You cannot force a change in how you feel about your stepson, but as all your children get older I think a change will happen organically anyway. Please be kind to yourself, and forgive yourself, you have NOT done anything wrong.
If you have managed to get to the end of this post OP, Thank You, and apologies for it being ultra long, even by my standards.