I'm sorry for your loss. I get that this is a really difficult thing to process but I don't think it's a bad idea to focus on your other kid(s). They still have a chance at having a good life. Why not try and give it your all to give him/her/them a chance. Just don't be impulsive about it, this is a permanent thing, really really think it over, please.
Hindsight is 20/20. Even the best dads/moms/psychologists often don't see it coming. You are not a bad mom, you're just human. We don't notice or know everything, but.. we can learn. The "I could've, should've" es are really tempting to get lost in. I'm not the best with words and this all probably sounds a bit harsh (I don't mean to be). But try to see this as a learning experience and see the potential future of your other kid(s), they deserve to grow up with a mom who cares about them (which you clearly do!). We will never know what goes on in someone else's head, the best we can do is give them the best tools and advice to take on life, support them and hope they make it.
Whatever you end up doing, best of luck.