Help

I need some advice.
I gave birth 5 months ago and I'm pregnant again. Not that weird on its own. (Although)
But the situation needs a bit more context.
Our first child came about through... chance. My partner is almost infertile, yes almost, because apparently there's still something swimming around. (And I regularly forgot that stupid pill) The doctor already thought our first kid was a real miracle. So I didn't see the point in immediately using contraception. I was also hesitating about what to use and was still breastfeeding.
But eventually decided (after stopping breastfeeding) to get the pill. You have to take it on the first day of your period and I was just a bit too late. I thought, well, next month then.
So that day never came. And after being 4 days late I figured it was time to take a test. More with the idea of, then I'll be relieved that I'm not pregnant.
Our current situation is as follows: I have 2 children, aged 6.5 and 4.5, from a previous relationship.
That's not going so great combined with my new boyfriend. Or it's becoming a challenge...
Things aren't going so sparkly between us either. We easily have an argument once a week (and those can add up).
Our family and friends were already a bit against our first child, given how difficult it was. Which is a shame. Because we both realize it. We really love each other and when things are good we say to each other: why can't we make it work?
I really want to be a mom.
I miss my kids incredibly. I think being a mom is the best thing in the world. My feeling is, I'd like to have 10 (not really).
I only see my two eldest once a week and I cried a lot for a year because I missed them so much.
My youngest was more than welcome.
I feel okay with my family. It could be better, though.
I just found a new job. Where I'm quite indispensable. I don't think they'll be laughing either. Worse, maybe they'll replace me because they can't afford to lose me during maternity leave. (I don't mean dismissal, but rather demotion, which happens more often)
So abortion? I don't know. I couldn't do it with the previous 2 either. The middle one came anyway, while I was using the Nuva-ring! (Also suddenly the reason for the breakup)
My boyfriend wants it, but he also thinks it's way too soon. We really want some stability between us first...