Ultimately, nobody can tell you whether you should or should not have a termination. I think you should seek some specialised counselling either way. I think your marriage is most likely over, possibly for the best for both you, so you need to look at the future with that in mind.
Honestly, with regards to what you should do- I think you need to take a long, hard look at the reality of your situation and be very honest with yourself. I totally understand that, in a perfect world, you would want to continue with this pregnancy. However, you aren’t in a perfect situation, and you have to consider that being a responsible adult and parent is not always about doing what you’d ideally like to do; sometimes we do have to live with deep regrets because the alternative is worse. I think you need to carefully consider the well-being of the children you already have before anything else.
What will the impact of them be if you continue this pregnancy? Can you adequately house and financially provide for 5 children (or 7, in the unlikely event should your relationship with your husband survive this)? Are you sure that you can adequately support all 5 children practically and emotionally adequately? Do you have support- you’ll need it for you all to thrive? Do you think your husband would be supportive even if your relationship ended (sounds unlikely)- if not, do you have a plan for how to cope? If the answer is honestly yes (not “ I have no idea, I hope so”) to all of these, then do whatever it is that makes you happiest. If the answer is “no” to any of those questions, then I think you need to give serious consideration to having a termination, however much you’d rather not, for the sake of the children you already have brought into the world because as a parent you have a duty to consider their needs as well as your own.
However, I slightly disagree with those totally blaming op’s DH for this situation. I think they are both as bad as each other when it comes to the utter irresponsibility of their actions resulting in an unwanted pregnancy. Given this, I have no idea why he is solely getting the blame for it as despite BOTH agreeing that they did not want more children NEITHER party has done a thing to prevent it happening. In that situation it is not the sole responsibility of either party as they are both having unprotected sex- presumably consensually as op does not mention coercion or deception- and they are both well
aware of potential consequences of that because OP has already had a termination.
Inevitably, given the reality of biology, OP bears the physical (and emotional) brunt of the pickle they find themselves in- whatever route forward she chooses- which is very uneven in terms of impact of the consequences of their actions on each partner- but that is the nature of pregnancy and something they were both totally aware of. Yet she still didn’t do anything to prevent a further “unplanned” pregnancy.
OP is not some innocent bystander in all this, she is not someone without agency or the ability to make choices. If her husband would not wear a condom or have a vasectomy, and she is genuinely unable to use any form of contraception, she could have sought sterilisation (am aware not straightforward/risk free, or always easily accessible), refused to have penetrative intercourse, or ended the relationship.
Yes, I agree his attitude is equally as bad- he said he did not want a child yet did nothing to prevent it. He is an irresponsible idiot, but no worse than OP. I do understand not every man wants a vasectomy, but that being the case he should have been using condoms every single time or abstaining from penetrative intercourse. He didn’t, which was utterly irresponsible, and now he’ll have a live with the consequences (financially, if nothing else )if OP chooses to go ahead with the pregnancy. No sympathy for him at all. But let’s not make out that OP is some sort of victim without any agency or responsibility in this situation.