Who was the man Eliza was walking towards home with, and why does she spit on him? What did he promise her?

She has become a prostitute and was going to perform a sexual act on the man in exchange for money, but he can't go on with it because it is too cold (which might be him substituting a fake explanation for the real one: that he likely wouldn't be able to perform due to him being too drunk).

When she complains that he promised to pay her, he rejects this.

When she asks how she's supposed to feed her children (now that she hasn't earned any money) he replies that he doesn't care since he isn't their father.