Feel very sad for you faced with this.
I think you need to decide what matters most to you, a relationship or children, and would the prospect of having a relationship with no children be more of an issue or less than having children but no relationship?
To be honest, NOT having or being able to have children would be a deal breaker for some men just as much as having children when you got together is for others.
You are making this choice for you, and if you go on to have a new relationship with another man then any children you do or don't have is part of the package that is you.
You are kind of thinking about this in a way where it's like trying to decide whether to have blonde hair or brown hair in case the next man that comes along likes one or the other. That would be silly wouldn't it? You make decisions based on your personal needs and desires and any man in your life will be the best fit to who you are.
I accept that you may feel it selfish to take this decision for you alone knowing that the baby you bring into this world you bring knowing that as parents you are separated. Even as a divorced parent I know how non ideal this feels, and how it hurts very badly to think that we are not giving our children the best life chances by being two parents together. Though lone parenting can be wonderful and children raised in this situation can suffer few ill effects, it is not what most of us would choose.
I guess you feel right now you have the chance to make the 'right' choice for your unborn child, and perhaps the 'ideal' of two parents together feels like it is the only choice that is right. Perhaps you feel that lone parenting is acceptable and fine but not something one would actively choose for selfish reasons of needing to parent a child.
Just remember, marriage/partnership is a social construct but that there are many ways to ensure that children experience the perhaps evolutionary need to be raised by both males and females and to feel the rich tapestry of love and guidance that is represented by being cared for and nurtured by more than their mother.
You can make the choice to carry on with the preganncy both a selfish one that fulfills your personal needs as well as unselfish one that fulfills his/hers but it takes commitment and support from others. If you feel you have this then don't be afraid of bringing your baby into the world. It would not be a disservice to him/her.
This is so not a black and white choice, therefore no decision is 'right'. Take comfort in the fact that you are protective of this baby's needs to the extent that this is a hard choice for you to make and know that you will have chosen as wisely as you felt able.