Thank you to everybody who responded, I appreciate the perspectives!
To the PP who has found it overbearing with a difficult baby I'm so sorry you're struggling, from what I can see here it does get easier and I hope it does for you, soon.
I remember when my DS was first born, for a week it was bliss and then he cried constantly too! He had colic, screamed constantly, hated sleeping in his moses basket, would only nap for 1-2 hours maximum and i dare say it was awful. Looking back at those not-so-distant-days I did wonder how I'd get through it but he grew into a very easy baby eventually. I'm hoping DC2 will be an easier newborn but even if she/he is not I'll have faith that its only a temporary stage.
I've read about the fourth trimester theory and thought that made a lot of sense, by the end of three months DS was like a different baby (although babies vary, of course)
I didn't get much sleep last night due to over thinking, not in a dreadful sense but trying to play through different scenarios in my head about how things could be with the baby.
I'm not against abortion to the extent I'd ever judge others for being able to make what is clearly a very hard decision, I admire their strength, but for me personally I know I'd never get past the "what ifs" and I'd struggle to deal with the guilt (more guilt!)
As you can probably tell I'm %90 percent set on keeping the baby, I just need to give my head a shake and stop projecting my guilt onto DS. Bless him.
To answer the PP who asked whether perhaps I see us as a team more so because ExP and I have split, I would say that is entirely possible yes 