I am 40 and DH 42. My kids are 15, 10 and 5. I am due another in December. I am pro-choice- no agenda either way.
I have known many mums who decided to start their family once in their 40's, or are adding to their existing family. You would not be isolated or unusual, and will make friends of other mums of all ages. The oldest mum my midwife had on her books was 56.
MY kids have been positive about it. The teenager relatively indifferent, 10 yr old thrilled, 5 yr old excited but thinks the scan photo is "YUK":)
My DH is a much better Dad the older and mellower he gets. He runs his own business as well so can be a little more flexible re childcare and family time than when he was young and starting out.
It is an absolute gift to have a healthy natural pregnancy after everything you have been through, something I think you might regret if you lost the chance. I think you are trying to deny to yourself, for good practical reasons, that this pregnancy is important to you. Therefore, I think the reasons for termination would have to be pretty overwhelming.
So, in that situation deal breakers for me would be if it would 1) be actually risky to your own health (including mental)
2)cause serious, far too life altering, financial problems to the extent you feel your existing family would be harmed.
- would cause more than a bump in the road of your marriage, but more an end of the road in an otherwise happy marriage.
It seems to me from your OP that you feel isolated and alone anyway, and are looking at a way to reconnect with the world (and your husband) apart from in the mummy role. I think relationship counselling sounds like a good idea here, as you are making all the sacrifices, and whatever you decide now might rebound on you later.
I am not explainig very well ( not a counsellor!), but what I mean is, you should decide what you want and unless DH is likely to walk straight out of the marriage and won't go to counselling, and you are not prepared to deal with that, then the decision should not be based on whether he feels "too old" or doesnt fit with his friends, or just to make life easier.
If you feel it would make you feel unwell, unhappy and resent being a mum again, I think you need individual counselling to help be at peace with your decision.
{{}}As this is hard on you either way, and so personal.