OP, there are single women who deliberately conceive a baby using a sperm donor and plan to be single mothers.
People have differing views on the morality of that, i.e. deliberately conceiving a child without a father, but I think, or at least hope, most people would agree that they love their babies and want to raise them to have the best life possible.
You haven't deliberately conceived a child without a father. You are pregnant, without it necessarily being planned but without either of you having taken steps to actively prevent it, with a man you were living with and planned to have children with some day. He, unfortunately, has changed his mind after the event. You can't do anything about that, but it is not your fault.
Now think about the kind of life you can give a baby. Think about the practicalities of where you will live, how long you will be able to take off for maternity leave, what sort of childcare you envisage afterwards, whether or not you have support from friends and family to help you raise your child, and if you don't, how you can go about finding a village for yourself. Imagine yourself and your baby, living together, spending Christmas together, imagine yourself feeding and clothing that baby and taking them to school and helping them with their homework and going on holiday and to the beach and trips to the petting zoo.
Imagine the kind of life you think you can realistically give your child, and then ask yourself whether you genuinely think it would be better for that child not to be born. Because personally I doubt there is anything about the life that you would have together that would make your child wish they had never been born.
There are plenty of perfectly happy children being raised perfectly well by single parents. There's no reason why that can't be you, if you want to go ahead with this.