Just broke up with a boyfriend as well, except it wasn't what I wanted at all. He just stopped being in love with me, which is excruciating.
But enough about me. I have never felt good about decisions that I've made out of fear. I know it's really difficult and horribly unpleasant, and I don't know if I'd be able to do the right thing in your situation, but you shouldn't stay with someone just because you're afraid of being alone. Friday nights can be rough. I guess the thing that has helped me the most since it happened is small acts of kindness and connection: people reaching out unexpectedly, even in real small ways. I can't deal with anything romantic right now, but it helps to know that there are good people out there. Because there are. There always are. There are so many people who are capable of unexpected empathy and kindness. I know this is hard. Try to be brave.