If that's you SP, although I don't normally suggest that people abort their babies, if you were my sister, I would probably suggest that you think about a termination.
This is SO complicated. Unless you feel strong enough to start again, not just are you strong enough, but financially? is it possible?
If it is, and you are in a positive state of mind and you have the support of your family, then by all means, have this fourth baby.
BUT...... if you aren't 100% sure you can be a single mum to four children, aren't sure that you have the support of your Mum and your friends, and if you are still this uncertain whether to OM is really there for you or not...then really I would consider a termination in your shoes. Ihate to say that to you because I wish I could think of a better happier ending.
Your OM had a bit of excitement, and paid the price for it, his wife KNOWS and he STILL went back to her. He had his chance to start again with you and he has not taken it.
If you were my friend I would be there for you. Do you other people in your life who could support you besides your mum? If you have this termination to please your husband do you think you can go back to playing happy family?
Don't have the termination for your husband, or for your Mum. Have the baby if you feel positive and strong enough and able to cope, practically, emotionally, financially..
GL
xxxx