I think part of the problem is that you probably haven't experienced parenting in a committed, stable and supportive relationship, so you'd probably don't realise how important it is. After all, you managed without that with 1&2 right...
A relationship that you choose to have kids in shouldn't be unstable. It should have enough history behind it that you can be confident of it lasting. You need to be sure enough of their character, of how hard working they are, of how trustworthy they are, that you know it will be an equal partnership...
I've had a look at some of your previous posts, you clearly aren't in great physical shape either which is having an impact on you, are on a programme to reduce the risk of you developing T2 diabetes, which is alarming at such a young age. You've had issues with drugs and alcohol in the past, an unstable childhood (no criticism, it just furthers that you've not have much experience of stability). It's not that the first day abandoned his child, but you don't know who the dad is. This isn't many to be a criticism, the fact that you're in a semi stable relationship at all after the start you've had, is awesome, but I think it's masking the fact that a 2y one-off relationship is too unstable for more kids.
It's not never, just not now.